It is simple why there are not more such games, they are very hard to make and very unpopular
instead of making one 3D game in 2-3 years you can make 2-3 simpler 2D games
I guess it depends on what you mean by 2d game, if by that you mean the RENPY swarm then yes.
I have not played your game yet, just because it only came up recently so I usually wait a bit to play new games like that(because often they don't have much content). It might be a lot more complex than this.
But, if you look at the map design in R-life it's fairly simple and not that big. Then he just put a first person camera and let that be the player, the player doesn't have a body in this game, not that it's bad for what it is but it's simple. You can rig that up in your engine in no time at all. Same with the enemies, they are fairly simple and I doudt he made them, sex scenes likewise are just a character model moving backwards and forwards(I mean there is bit more depth than that but still). Those character models he didn't make either, you can tell by the difrence in artstyle and physics engines on each character(velvets breasts shake, the others don't). The story and character interactions are simple as well, everything about this game is simple.
So sure, it can be complex to make a 3d game but if all you are doing is making a camera move through a simple world and all your character models(and probably attack animations as well) are made by somebody else then it's not that much.