It comes down to there isn't a lot of truly creative thinking going on in the entertainment industry. They find something that works and then run it into the ground before they move on. Anything new that becomes a hit becomes the template for the next couple of seasons. TV. Music. Movies. The trends all run in cycles. Right now it's gay people. Writers think gay people are funny to straight people, so here they come. Writers also tends to use stereotypes so that they don't have to do too much thinking about character development. That's hard work and takes a lot of time, which you don't have when you pump out a show every week. This is the difference that makes the good shows last: talented hard-working writers.
The other thing that decides what we see is money. That's why reality shows are everywhere: they cost very little to produce and can rake in big advertising dollars. No big stars. No permanent sets. Small writing staff. A TV mogul's dream.
Going back to part of the original post. You know who buys 99% of lesbian porn? That's right: straight guys. Why? They dream about themselves in the middle.