Someone already covered the vague idea of it. But just to nail some points.
A lot of adult games use the same “engine” for visuals, named Koikatsu. Some I can name from the top of my head include but are not limited to:
- Hero’s Harem Guild
- Champion of Realms
- Goddesses’ Whim
- Lessons in Love
Haven’t played any of them, but I see them mentioned often. And they seem to have a relatively large following.
But yeah, there are plenty of assets that are potentially going to be reused unless the devs took their time to make their own 3d assets for clothing, environments, etc.
Also I might add that CK started development in June 2019. The itch.io version was first uploaded on the second anniversary.
Make what you will with that info.