Social nods, a.k.a. pandering
E.g., the way every tv show or movie needs to have a gay reference. Westworld or Game of Thrones having two guys getting it on.
Same sex couples are, what, only 1% of the population? By numbers, there's other marginalized groups with more representation in the population, yet they never get represented in television or movies.
So what determine's who gets written in to a show? Is it based on purchasing power (How much money as a group they have, making them attractive to advertisers?)
Or is it more basic: Every screenwriter simply follows what's trendy?
Everyone talks about gay marriage, so they write about it and make shows about it. No one talks about Native Americans, so nobody writes about them or cribs them into shows.
The latter would mark screenwriters as even bigger pop culture whores then the general public, imo. Taking their marching orders from Operah and liberal trash mags...