NSFW games aren't even real "games", nobody is playing them with two hands.
That's an unfair statement. People seeking what you think they seek can just go to a regular nsfw site that even has real people. No game play needed. Coincidentally, the most popular topic on those sites is "family". The very incest topic that is now forbidden in games, due to payment processors demands.
Do you also think that any reader of raunchy pulp romance novels reads with one hand only? And what do you think people do, while watching Game of Thrones?
It is rule34 in action. Games exist, so there is nsfw games. I am an adult. Why should I play Mario, if I can play Mario with blackjack and the other thing.
Many adult games are not good games, but that is true for most regular indie games here too. Ever visited the popular section with all those horror games? Why do people play games that are scary and have blood in them? Because it is thrilling. Know what is also thrilling? Adult games.