If you think people don't make games with deliberate Incest then you should see (Such a Sharp pain) where the father will make him 9yo daughter to sick his cock
Full incest exists, for sure, but are they on this platform? For example, when I look up "Such a sharp pain",I don't see it on itch.io. All I see is a patreon and some sketchy sounding websites. I would guess that people avoid incest so that they can reach a larger audience
But (Being a Dik) isn't on itch.io and it's one of the most popular renpy games out there and i don't think they're trying to hide anything in the game