I don't think the "LGBT" tag is given any special treatment by the system. The "adventure" tag is because it denotes a genre, and genre is specifically tracked. But tag popularity also factors in searches; one that's only used for a few games might not be returned. "LGBT" happens to be frequently picked by creators, because it's been around for a while. If you can convince people to use "LGBTQIA+" more, I'm sure it will start showing up as well.
Viewing post in Updating LGBT tag to LGBTQIA+
At this point I'd argue that LGBTQIA (or any variation thereof) is practically a genre in itself now. The number of different games and stories we have coming through from the community on an almost daily basis in different forms speaks to that.
Maybe we need to have these games as their own genre now???
Anyway, I've made a push to have folks tag their games with LGBTQIA and/or queer to help boost visibility. Does anyone know how many games need to be tagged with something before it will show up in the search bar?