Yeah, if you like the art style, genre, and strategy games, they're probably worth a play. As far as strategy porn games go probably some of the best available other than maybe the Rance series? Though I haven't really played much of that yet.
I'd wager it's probably because the effort required to create such a game just doesn't scale with the average intended. Any R18 game is going to have a much smaller market to begin with. Further still, R18 markets are probably quite heavily further segregated into various kinks. So right out of the gate your available audience is being filtered quite a bit. And it doesn't really matter what format it takes, when it comes to porn, your essentials are the porn. Trying to work out a well-designed and balanced game tends to be secondary. Compelling story takes time to write, edit, revise, and proof-read that could've been spent making more erotic scenes. Good game mechanics and design take time to create, test, debug, and balance that could've been spent on making more erotic scenes.