I believe gay marriage being legalized opened up some sort of floodgate within many people's minds, and not for the better. They were like "oh, it's cool that people of the same sex get married? That means I can talk about all the shitty things I've been thinking about LGB and stuffing down deep inside, and it's OK now because gay is normal!"

It was a really weird shift in western culture, to be sure. I do wonder if that's a part of why we (as a society) have battles between liberals and conservatives so strongly now. Both thought some shitty things, but I've gotta say, at least conservatives back it up with facts and legalities. Liberals are backing it up with feelings and pseudo-science. Libertarians are an interesting blend of both, but don't have a consistent argument because of a lack of representation.

As to your question:

Why are LGB given the short end of the stick when it comes to creating representational media, when pretty much everyone else is being catered to?

LGB people don't actually matter, we are pawns in political games. That includes media - television shows, live news, articles, etc. It's not even about LGB specifically, we're just a label and statistic that's able to be used now. The tail is most certainly wagging the dog in western countries, and THAT's what our real fight is against.

Instead of asking "why aren't LGB", ask yourself "why trans/non-binary/etc are". And then ask yourself "who and what is doing so".

It will take time, and you will go down a rabbit hole. Recognizing that our media and celebrities are promoting it, that's a good first step. Pick your favorite news company or celebrity, and start digging.