I saw a 4d game here :-)
But I believe the question in general is more in this direction: most devs use an engine and there are 3d engines to use, for those who do not have deeper understanding. Or rather, most do not even have a 2d understanding of their game math. So if they use an engine anyways, why not use one of them 3d ones.
I mean, there even is this rpg paper maker, that is in 3d, even though it is still pixel art.
Maybe there is an anomaly/bias in itch users, and the amateur 3d game makers are just elsewhere. Like making mods for Minetest or Skyrim.