Except that TASM is an origin story, and should be based on the original comics. If they wanted to show a different Peter based on later stories, they shouldn't have wasted their time on Peter's origin story in this film, and just have him start off as Spider-Man, maybe with flashbacks to Ben's death.
Actually considering we got an origin story 10 years ago, making another one was just wasting screen time, since the 2002 film portrayed Spidey's origin almost perfectly. But giving him a different personality than the 60s/70s version is just another reason.
Sure we can. A lot of people do. But a lot of other people don't because they have different opinions. And that's okay.
Where does it say that the original comics should be the only inspiration to a comic book movie adaption or introducing the origin/universe to a new audience? No comic book movie is 100% faithful to the original comics no matter what some fans wish it to be. It's a specific cast and crew's interpretation of a comic book character and his universe, especially one with many years with different writers, artists, etc working on it like the following examples:
Avengers/MCU heroes(Hulk, Iron Man, Captain America, Thor, etc) is a combination of the Ultimates and Avengers(both classic and modern) comics with a few twists to keep it interesting and fresh
1978 Superman, Man of Steel, Batman Begins and 89 Batman weren't 100% faithful to any of the Superman mythos
no X-Men movie was totally faithful to the comics
Tim Story Fantastic Four movie had classic and Ultimate elements to their movies
Ed Norton Incredible Hulk was in a sense can be seen as an origin film but it was more like the Incredible Hulk TV Show with some Ultimate and 616 elements
If TASM wasn't faithful to the comics, Sam Raimi Spider-Man was not exactly faithful to the original Spider-Man comics minus following plot points and recreating a few comics panels either(Peter and Mary Jane knew each other since they were kids and live in the same neighborhood, Peter only becoming a wrestler to win MJ's love, Dr.Connors being a physics professor, Peter shoots organic web, Peter meeting Gwen after he met MJ, Eddie Brock Jr's name and build Harry being Peter's high school friend, Green Goblin being the first super villain Spidey said instead of Vulture or Chameleon or Doc Ock, Doc Ock being connected to Oscorp, etc). It wasn't more or less faithful than the Amazing Spider-Man.
even the most faithful comic book adaption movie(Baron 1990 TMNT movie or 4Kids TMNT cartoon) wasn't exactly similar to the original comics or cartoons.
The Amazing Spider-man I thought it made sense to do a new origin because it doesn't creating a new universe and had to introduced their interpretations of their character and their Spider-Man universe which is almost radically different from the Spider-Man universe Sam introduced in almost every way and the Incredible Hulk and Punisher did what you suggested and had some fans as well as people who watched the movie confused if it was a sequel to the previous movies so if that could happened for that movie, the very same thing could have happened if they did that Spider-Man movie.
Honestly except for a few plot points and comic storylines I don't think Tobey Maguire/Sam Raimi Spider-Man movie was any more or less faithful to the Spider-Man comics than Andrew/Mark Webb's movie was honestly.
He is in no way a fifteen year old.
That may be true but there are more similarities to Ultimate Spider-Man(as well as to other Spider-Man comics) than differences.
For example, Oscorp in the Webb films feels like a combination of four important companies with evil rich bosses connected to Spider-Man(well to be more specific Ultimate Spider-Man: Roxxon, Oscorp, Hammer Industries and Trask Industries) but there's not many other fictional successful Marvel Companies that has ties to the Spider-Man universe that Marvel can use except for Tricorp or Horizon.(looking mainly at Ultimate) and we're talking about Spider-Man villains who are animal themed and related to science in one way or another, it's kind of made sense that some writers did it(at least it's not like how John Byrne or JMS handled it in their respective Spider-Man comics):
Kingpin - IDK if he's owned by Marvel or Fox studios by now but I know Sony doesn't have any rights in using him for the moment. In this show, he is the most recurring villain. This Kingpin is fairly close to the comics version, but he is often occupied with manipulating superpowered characters to do his bidding. He's the mastermind behind the creation of the Spider-Slayers and is responsible for the creation of the Insidious Six, the animated equivalent of the Sinister Six and also was part of the creation Black Cat and the Spot among other supervillains.
S.H.I.E.L.D.- basically S.H.I.E.L.D. and to a lesser extent Stark Industries and the super soldier serum(for more genetic experimental characters like Cap, Hulk,Red Skull, Abomination etc and in the Ultimate Marvel universe ties a lot of superheroes and supervillains origins together including Electro, Green Goblin,Spider-Man,Doc Ock, Sandman, etc) in the MCU is what Oscorp is in the Mark Webb Spider-Man movies and connecting different comic elements together to make a more cohesive universe and same goes for recent cartoons, and comics Ultimate or otherwise but Marvel Studios own that.
Oscorp - in most recent comics and media Oscorp has some pull in one way or another, connection to a lot of Spider-Man characters and story elements and what goes on in Spidey's life. The 2 of the most famous Spider-Man villains I see the most that are usually connected to Oscorp and Norman Osborn in modern media in one way or another is Otto Octavius/Doctor Octopus(in in the 1990s Spider-Man TV series, Otto Octavius was Peter Parker's science teacher at science camp when the youth was 10 years old and Otto was working for the Hardy Foundation when he became desperate to finish his experiment, Ultimate Spider-Man and Spectacular Spider-Man cartoon has Otto work for Oscorp, Ultimate Spider-Man comics had Octavius work for Oscorp and a part of the accident that created Spider-Man, Green and Hobgoblin and Doctor Octopus, and Spider-Man 2 had Doc Ock funded by Oscorp) and Adrian Toomes/Vulture(Spider-Man: Noir where he was taken by mob boss Norman Osborn (The Goblin) to become one of his hitmen, Ultimate Vulture worked along with Norman Osborn's Sinister Six and both 90s Fox cartoon and Spectacular Spider-Man cartoon wanted revenge on Norman for rejecting his work). Ultimate Spider-Man comics had tied it in to the origins of 4 superhumans and Nick Fury in trying to recreate Captain America and even was able to create mini bunkers and spy on Spider-Man/Peter's life, Spectacular Spider-Man cartoon had Norman Osborn/Oscorp tied to multiple characters in different way(Rhino, Big Man, Shocker by tipping him off to Tricorp Shocker suit, Chameleon, Sandman, Molten Man,Doc Ock, Vulture, Doctor Connors by having some pull on bringing Peter and Miles Warren into his lab, Mac Gargan,Morris Bench, Miles Warren who Norman was able to get to join Dr. Curt Connors' team at the Empire State University lab., etc) on the show in one way or another(you can argue the TSSM cartoon has some influence on Mark Webb movie as well), the MTV Cartoon had Oscorp be the reason Dr.Connors lost his arm and he holds a grudge against Oscorp(which also had similarities and also could be also inspiration for Webb Spider-Man film and Brian Michael Bendis has some influence on both movies), Fox Kids 90s animated series Oscorp was constantly under the influence of the Kingpin to create weapons for him and was tied to the Smythe family, Hobgoblin and the two Green Goblins and bought Adrian Toomes’s company and it's board members included Anastasia Hardy, Wilson Fisk, J. Jonah Jameson. and that's not even bringing up 616 or the Ultimate Spider-Man cartoon. Raimi films had Oscorp/the Osborns in one way or another be connected to three out of the five supervillains in the movie from the creation of the Goblins and the funding of Doc Ock's work. Norman and Oscorp in recent comics always has some times in some ways to Spider-Man villains or something that happens in Spidey's life(like Flash was driving drunk in an Oscorp truck with give him brain damage). It's the most well known business connected to the Spider-Man mythos and one of Spider-Man's biggest and well known villain and has been connected to other Spidey baddies so it did made a lot of sense
Hammer Industries- Ultimate Spider-Man wrote it as Hammer Industries intentionally created both Electro(Sold it to Kingpin) and Sandman and hired Doc Ock as a corporate spy who came for revenge, but Marvel Studios owns the rights to use that company in their films especially since it's more connected to Iron Man for the most part
Roxxon -Responsible for being connected to a lot of the supervillains that Spider-Man faced in the Ultimate comics, he is targeted by a former employee who took the identity of the Tinkerer. Donald Roxxon hires Silver Sable to track down Spider-Man, as he believes the hero knew who was responsible. He also wants to know why Spider-Man seemed to be looking out for Roxxon (Spider-Man had actually not been but a series of coincidences led to the appearance otherwise). Silver Sable captures Spider-Man and brings him to Roxxon, who unmasks and interrogates him. Spider-Man escapes Roxxon and ends up saving him from the Vulture. Among those who attacked Roxxon are Killer Shrike, Omega Red, Vulture, and The Spot with the former three being hired by Tinkerer and the latter one being created in an accident at Roxxon. It is also revealed that Herman Schultz was also a former employee of Roxxon Corporation, whom Roxxon got to design weapons before terminating his employment at the company, leading him to a life of crime. Schultz also stated that even if Spider-Man was able to bring down Roxxon, "two more would grow in its place" (which is similar to the motto of the fictional terrorist organization HYDRA). There is a Roxxon Brain Trust consisting of Doctor Octopus, Dr. Arnim Zola III, Dr. Layla Miller, Misty Knight, Dr. Samuel Sterns, and Dr. Nathaniel Essex and has secretly assembles several teens(like Cloak and Dagger,Spider-Woman, etc) to use as guinea pigs in their experiments to create super-soldiers (such as Bombshell and Cloak & Dagger) as well as restoring the Venom suit. For all intents and purposes, it can be compared and seen as the most similar to the Webb interpretation of Oscorp but again Marvel studios owns the rights to use Roxxon in their movies/TV shows.
Trask Industries - connection to Peter and Eddie's dad as well as Adrian Toomes and the Ultimate Spider-Man video game R.H.I.N.O., Beetle and other events but Fox/X-Men owns those rights and using that and it's another company extremely similar to Webb Oscorp
The point is Utimate is the Marvel version of Elsewords.The Lee/Ditko era is always going to be the default version to go to,because it's A) The Original. B) Better
While you may not like the Ultimate Marvel it has introduced ideas that works for adaptions for a more general audience(cartoons like Spectacular Spider-Man or Avengers: Earth Mightiest Heroes, movies like Iron Man or Avengers) among other cartoons and movies as well.
Ultimate Marvel's original intent was to streamline and modernized the original Marvel stories in order to make it more access the then 38 years of multiple storylines, some writers (such as Mark Millar) had said in one interview
Mark Millar Shares His Thoughts On THE ULTIMATES Influence On MARVEL'S THE AVENGERS
The Ultimates was the book I wanted to write when I started at Marvel eleven years ago, but the Avengers characters were regarded by management as less commercial than the X-Men and so they offered me Ultimate X-Men instead. The idea was to re-invent their characters for a modern audience and X-Men launched at number one so they trusted me with the Avengers revamp. Even so, they still tried to talk me into a Wolverine book instead as Cap, Thor, Iron Man and Hulk were all, in the company’s eyes, a little less cool."
"But I always loved them and used what capital I had at the company to push this through and Editor In Chief Joe Quesada was very supportive of me. I told him I wanted Bryan Hitch on art, even though Bryan had just signed with another company, and they moved Heaven and Earth to get him on the project. We really just took all the elements that made The Avengers hard for a mainstream audience to accept and streamlined all the characters into a single book, bringing them under the command of Nick Fury to pull the whole thing together. I’d wanted more ethnically diverse characters in the line and made Nick Fury black, but it was Bryan who came up with the genius idea of Samuel L Jackson to be the face of the character’s reinvention."
"Our first storyline was basically Independence Day with superheroes and we took the Chitauri aliens from the David Icke books and made them the bad guys, Loki being the the villain from our second book. Kevin Fiege (who runs Marvel Studios) was a big fan of the books and told us it made him realise an Avengers movie could actually be a lot simpler than they’d thought and so they used book one and the ending to book two as the template for the movie, which is enormously flattering. People have suggested we should feel ripped off, but we don’t own these characters. All we did was give them a lick of paint and come up with a story and the visuals. These are Marvel-owned characters and I have my own little empire with Millarworld so I’m genuinely just pleased to see all this on the big screen and wish them nothing but the best with it."
Ultimate Marvel has brought ideas(origins, stories, costumes, etc) that is a lot of Marvel Movies has utilized in their movies