Honestly, the main problem for Boba Fett is that Din Djarin exists. It means his character has become a bit redundant.
We're talking about a mysterious bounty hunter in Mandalorian armor (made from a very particular type of metal) who utilizes cool gadgets. He generally doesn't take off his signature helmet, which is why his voice has become such a big part of his personality. He chooses his words carefully but also has pretty snappy one-liners. Born during the prequel era, he lives by his own code, killing if he has to (but not because he likes to). Eventually, he takes on an unexpected father role, showing new dimensions to the character.
Before Mandalorian, all of that was Boba Fett, with the last line mostly referencing EU stories. Now, it refers to Din, assisted by the adorable breakout hit that is Grogu. Which I guess is why they tried a different direction for Boba.
It didn't work well, but I can see why they felt it was necessary.