The Badger wrote:
He stated that he quit because he was unhappy that the role of Batman was being increasingly over shadowed by the bad guys and sidekicks. http://www.ew.com/ew/article/0,,291605,00.html
It's also been claimed that whilst on the set of Heat one of his co-stars (either Al Pacino or Robert de Niro, I can't remember which) ribbed him mercilessly for appearing in a comic book, kids movie.
That was a rough time for comic book movies. High brow actors frowned on it.
Only those actors that didn't mind doing a "silly comic book" movie would sign up.
Now it's different with comic book movies getting Oscar nominations