I think the issue is passion for the project alone won't see it through. Games are very dense, which is what makes them great for consumers, but it also takes a toll on the producers, who have to implement all of it through hard work. Even procedural systems, which help offload the work greatly through clever tricks, need a lot of hard work to make work correctly, and then they usually are lacking against a hand-designed experience (Which can be worth it, for plenty of games. NMS and Spore make great use of procedural systems for example. But they're still hard to work on).
It's also artistic, and over half of all artistic projects of any nature die before they're out of the womb. Here in the indie game space, where most porn games are, we have a unique insight into the artistic process that most people never get to see, so we see all those aborted starts and failures that you usually don't see. Even the most ardent Stephen King fans don't get to see into his wastebasket to uncrumple all the started books he never finished or published. Some of them are probably quite intriguing, but will never see the light of day for reasons the consumer may never understand (or even King himself, art has a habit of outgrowing the artist).
Games combine traditionally art stuff like the creative process, with highly technical stuff like code blocking, and it takes a very particular type of person to get into the thick of that morass and produce something. If you do, then great, the consumer gets the best of both of those worlds. But you as the artist need to suffer the worst of both worlds first.