Because one of the main rules of Hollywood is "you don't cover up the face of the star." They are whom people come to watch. Studio execs HATED Harrison Ford in a thick beard for The Fugitive for the 1st 20 minutes but - it was Ford's idea and he's someone NO ONE pushes around once he's signed on - especially at the peak of his career in the early 90s.

Also - many actors just want nothing to do with lots of prosthetics. Jim Carrey said never again after the hell he went through playing the Grinch, especially the green contact lenses where the studio brought in a therapists that specialized in torture victims to help him get through the filming with the contacts. But - Jack Nicholson would just fall asleep in the makeup chair when he was getting his prosthetics to play the Joker in Batman. So for him it was nbd