It's very similar to sports; there are many more people who want to work in sports than there are jobs available, so the ones that do end up with jobs working for a team are overworked and underpaid despite being in the top single-digit percentile of applicants. I imagine the same is true for other entertainment industries, but I don't know enough about them to comment.
There are, of course, people in these industries who do have bargaining power, but it's a very small minority of those with outstanding reputations.