A mega-star like him, cruise, will smith, johnny depp, etc... is excessively expensive and BUSY BUSY BUSY
Brad Pitt's average payday on movies is less than John Favereu got
paid to direct Iron Man. Also, he's done about 2 flicks a year, which
is actually less than RDJr, who does about 3 a year (albeit smaller
indie flicks usually).
These films hinge on their actors working in the part and I'm more
than willing to have an amazing film that I have to wait 4 years for
a sequel to if every film that comes out is amazing and classic.
Also, both Norton and the Director have said that the "issues" were
entirely blown out of proportion by the online media, and that only
happened because Norton is a very talented screenwriter who Marvel
hired to write the script as well as star.