Don’t be daft. These people dream of making movies and love doing it. They know if they don’t do it under the terms the studio demands, the movie doesn’t get made. They have no leverage and will be replaced by someone willing to work on the studios terms if they don’t agree.
So they can either work in a field they are very passionate about and be exploited, or do some soul crushing bullshit job in an office like the rest of us.
Because it's an oligopolistic system. Either you go through them and get your movie made, and maybe people will go see it, and maybe you'll get yourself some money. Or you don't, and get nothing. That's why, in many countries, cinema is subsidized by the government (in extenso, it's paid for by the people of said countries).