It seems like when the website lunches, the first game that get popular that has a certain genre, that genre get applied to the website. And everyone keeps recreating it. That's just my theory though.
Yeah, maybe people who go to a site often get inspired by the games they like and make their own, and maybe some devs think "right, this is popular, we need to release games like this..." (alternatively, they might say "our game isn't like that, so we won't release it here").
