Film director here. I'd recommend spending some time Googling "Hollywood accounting".
It's EXTREMELY common for directors to get screwed out of profit deals on films - so much so that the default advice to new film directors is "assume that you'll never see any money from your points on the deal, no matter how profitable the film is."
Peter Jackson's case is not unusual because he was screwed, it's unusual because he fought so hard and so loudly.
I also dislike the implicit assumption that the category of "people who make movies and TV" is "directors". Some directors take a major role in production. Others are tools in a chain, albiet important and highly paid ones. There are lot of people who bring about movies and TV that aren't directors. Vince Gilligan rarely directs, for example.
Now we've crossed into fantasyland, of stuff you've just made up because it flatters your viewpoint.
Film studios provide enormous amounts of resources for the making of movies. Furthermore, it's common for movies to be part-owned or whole-owned by people involved in their production. It's not like the music industry. Top producers, backed by lots of monetary and social capital, make these shows happen. Often writers and directors are also producers. Sometimes people get screwed (famously Peter Jackson) but this seems to happen to few makers with critical jobs, and you'll note he didn't get fooled again.
Of course it is not the case that assorted writers and actors and artists can get together and make a hit show with no expert knowledge. TV shows are very, very hard to make. We're not talking about an exploited proletariat of TV show makers here.