When talking to someone who works on set, it's interesting to know that unless your a DeNiro or Pesci or Baldwin level actor, he's worked with all 3, 2 were a holes, word gets around. I'd say, IF Zack was truly hard to work with, big budget movies don't want to put up with the nonsense. Making movies and TV shows is a lot of work and money. So, the producers and the casting managers typically avoid even having these folks read for roles. So, to answer your question in a long, winded way, the latter. Interesting add, my friend is based solely in NYC, so there are probably other actors dealing with these problems as well, especially those that shoot on locations or are shot in LA. Zack might have more "connections" being in LA, and it's possible that the powers that be are okay with him being a douche of a person.

My best friend works in the industry, in front of the camera. Saw him in October. He was and does work on major TV shows and movies. Asked him in 30 years of doing this professionally who was the worst to work with, and he said without hesitation. Zack Braff. I said no way, and he said he's acts like an entitled a hole and pretentious as hell. And I thought of 6 or 7 folks before I asked the question.

However, I still love Scrubs and Garden State, but it does make me look at a few scenes with a little more scrutiny.