Consider that:
- The game is developed by one person.
- It´s a dark fetishist hentai game (meaning that the game won´t aim for general audience).
If you compare this game with other game like Rimworld, Dark Souls or any game in the catalogue of Steam that cost 10 times less, obviusly you will think that the game doesn't deserve to be valued in 30$, but this game is not a regular Steam game. It's a dark game that is very rare to encounter and definitely not a vanilla hentai game.
So, that is my personal explanation for ''why this game cost 30$''