I think that's pretty much all games like this.
Most, yes, but not quite all. Secretary is on schedule to be completed next year. Perverted Education is backfilling content that patrons have asked for but most of its endgame stuff is done. The Sissy Girlfriend Experiment is still going strong and the only reason it hasn't been completed is that their patrons keep asking for more content (they don't want the game development to end). That's three exceptions right there (four, if you count The Whore of Babylon, which was completed, but I don't consider that a real TF game).
It's hard to stick with things long term.
Some devs just lack sufficient determination to overcome burnout. Many just bite off more than they can chew. They realize too late that they lack the skill to do what their fans want them to do or what they originally planned to do, and their pride or finances block them from getting help.