Commercial implies "for profit", and there are a lot of compromises made and shortcuts taken in favor of this. This usually rubs against the grain of idealists like myself. For example: the movie Brazil, had it's ending changed to a happy one in order to make it "more agreeable" with the general viewing public.

Commercial success for an artist is very difficult. A musician would have to appeal to a wide enough audience, while still creating what they wanted. A painter would have to gain critical acclaim before he can start charging higher prices. A lot of times, artists have their success only after they die.