It's your game, if you want an NPC/Character to be male, female, transgender, straight, gay, bi-sexual, asexual, a necrophile, a person who is sexually attracted to pete moss, than make it so.
First, it's kind of the epitome of jerkdom to put in necrophilia in the same sentence as, well, a lot of what you're saying. I'm going to assume you didn't mean it that way, and just put it there by way of making a joke.
Nothing is stopping you. I don't understand people anymore, they need to see this character created by someone else (in this case WotC) and published in an official book in order for it to be that? Why?
Because while you can do whatever you want - and no one in this thread has been contesting that, at all - it pays to have an official supplier of the product actually endorse that lifestyle choice. Do you remember years ago, when the TV show Ellen had the main character "come out"? That was a big deal - even though it didn't change anyone's actual life. Why? Because it showed that the TV networks were willing to accept the existence of homosexuals as main characters... before that, they were just "confirmed bachelors" or something silly like that.
Or think of the occasional gay character that shows up in Doctor Who (especially during Eccleston and Tenant's runs). It wasn't a big deal - just a line in passing. And in doing so, it showed that the series was recognizing the diversity of human life.
We know we can make NPCs gay if we like. But it's sure nice to see a bit of recognition in official products... which is an entirely different thing.
Why should time and resources be wasted to make sure there is a population proportionate amount of NPCs that fall into each category?
Time? It's pretty simple to, once in a while, flip things. No one's asking for a perfect demographic representation. We see a LOT of products where someone will "be influenced by the highest charisma female" or something to that effect. It's pretty easy to flip that and say "He'll be influenced by the highest charisma male".
In the most recent Adventure Path from WotC, Out of the Abyss, there's a whole slew of NPCs that will travel with the characters... and I can see a few that could be made homosexual or transgender (there is a hermaphroditic myconid, I guess...) It doesn't take any extra page count to invert the sexuality once or twice. Hell, they even mention a drow priestesses lovers... so it's not like wotc is avoiding the concept of romance or sexuality in their games.
So why not flip it?
Why anyone has to even keep count?
I don't know about you, but I can count to zero pretty quickly.
So the NPC bar wench is attracted to a dark and handsome male in the book, you want her to be attracted to beautiful blonde female elves instead in the name of equality...ready watch how simple this is...now she is, in your game, in your mind, in your players mind, who cares what the book says?
HOLY COW THAT WAS SIMPLE! MY MIND IS BLOWN!
Wait, no. We already knew that.
I'm going to invert your statement. How hard would it be for WotC to make that change on their end first? And if players don't like that the bar wench likes other wenches, let THEM change it? How come we must always focus on the "standard" when we're playing in a world of fantasy and make believe?
Ready? Watch how simple it is.
The whole purpose of this hobby is to be able to think out of the box, creatively and build the world you want, so do it, and stop worrying about what the example in the book says. It's not lip service, it's just simply WotC hoping you have enough initiative and intelligence to change things to how you want them for your game, while I change them for how I want them for my game.
So you're saying that WotC puts out a subpar product that they expect players will be intelligent enough to change to suit their needs? Because that's not how the world works.
You put out a product that you hope the customer embraces wholly. And you change what's in that product so that you can hit a wider audience. This is basic marketing. If you have a fringe product, you have a tight range of what's in your product. If you have a mass release product, you better hope it has enough in it to appeal to the mass. And that means you vary your approach in what you're putting forward (or you appeal to the lowest common denominator, which isn't how it works in games like D&D, thankfully).
It's a game. Not everything in the world has to be viewed through the eyes of social justice. Just because Lara Croft had a ridiculously tiny waist, huge boobs and swung around dungeons doesn't mean I expected my wife to fit that unreasonable image and she doesn't, and I love her exactly the way she is.
It's really funny you mention Lara Croft. Because they re-did her a few years ago in a new game. She's a completely different body type, still attractive but quite capable, and guess what? She did quite well.
"Social Justice" in entertainment just means that you try to stop appealing to just one demographic, and try to represent different groups as well - without resorting to unpleasant stereotypes. When you approach a game with this lens, you get new players. I don't see why D&D should be any different.
TLDR; If you want everyone in your world to be a hot transgender person than make it so, stop waiting for someone else to make it so.
TLDR - Stop trying to maintain the status quo out of fear of letting new people into the game. There's nothing wrong with the occasional trans or gay person in a game... it won't hurt you any. And if you don't like it, no one's stopping you from changing it.