So why, when searching "Gay" games on your website, are 90% of the games Furry
You are sorting for popular. So ask the people playing those games. Seriously. It is the same BS with the complainers that do not like horror games. It is on top of popular, because it is popular. You can go a step further. You will see those games, even when only filtering for adult games. On page one there is like half a dozen furry games. One of them not sporting the gay tag.
Also as was pointed out, tags here are chosen by the devs, not by itch. The tags are not even from a fixed pool of tags. Devs can invent new ones. That is why there is a gazillion tags for "non mainstream" stuff.