I think you're falling into the same trap as Sony in that everything has to be explained. Where was Joker from in TDK? Did you care? It just wastes time, time that could be better served developing personalities and motivations.
Well, I already stated that The Joker is the one villain that is able to break free of the mold of needing an origin to be a successful villain on screen. And as Doctor Octopus has so kindly pointed out, this was a mystery of that character from the comics. I will say that execution of these ideas is a strong point of the success but in TDK, they absolutely nailed it. No question, imo.
However, when we are talking about villains like Ock, Vulture, Goblin, etc. the more popular rogues from Spidey's universe, they definitely need a back story. And imo the "trap" that Sony keeps falling into, is not developing the villains properly. They failed to present the humanity of Connors by leaving his family on the cutting room floor. He is a perfect example of a villain from SpideyLand that absolutely needs an origin--however basic it may be, the whole point of his character is one of sympathy. You lose this by not presenting the elements of his human side. This completes the character and leads to a better understanding of his motivations and that's how the Joker is so different. He doesn't need the origin because his origin does not give birth to his motivations, whereas characters like Connors, Otto, Norman O., are bound by that, imo.
They can present all the characters as established already. I care about where the characters are going not where they are from. If the movie opened with all of the villains sat around a table discussing their next move would you care that you never saw how they got to that point? I wouldn't.
Alright. So let's play with this idea.
What
is their next move? Rob banks? Take over the world? And more importantly, why should I be interested in what they're doing?