Por que a Marvel decidiu reformular Bruce Banner em Avengers?

Ele supostamente não se dava bem com os outros

We have made the decision to not bring Ed Norton back to portray the title role of Bruce Banner in the Avengers. Our decision is definitely not one based on monetary factors, but instead rooted in the need for an actor who embodies the creativity and collaborative spirit of our other talented cast members. The Avengers demands players who thrive working as part of an ensemble, as evidenced by Robert, Chris H, Chris E, Sam, Scarlett, and all of our talented casts. We are looking to announce a name actor who fulfills these requirements, and is passionate about the iconic role in the coming weeks.
- Kevin Feige talking to Hitflix

Ed Norton falou sobre essa questão em uma entrevista com a NPR . A resposta muito curta é que ele não gostava muito do aspecto "roadshow" de comercializar um grande tentpole filme e não estava disposto a comprometer.

“My feeling was that I experimented and experienced what I wanted to. I really, really enjoyed it. And yet, I looked at the balance of time in life that one spends not only making those sorts of films but then especially putting them out, and the obligations that rightly come with that."

Ele também afirmou que temia ser transformado em tipografia.

"There were just a lot of things—I wanted more diversity. I sort of chose to continue on my path of having a diversity of experiences. Maybe on some unconscious level, I didn’t want to have an association with one thing in any way degrade my effectiveness as an actor, in characters. I think you can sort of do anything once, but if you do it too many times, it can become a suit that’s hard to take off, in other peoples’ eyes. And if I had continued on with it, I wouldn’t have made Moonrise Kingdom, or Grand Budapest, or Birdman, because those all overlapped with [Avengers]. And those were more the priority for me, but I continue to be a fan and I’m really, really happy I got to do it once.”