Its because making porn parodies doesn't pay well, especially how often long it takes for a game to gain popularity and how much effort it takes. Even if it gains popularity most people pirate the game anyways.
You have to realize that Patreon takes a flat 12% cut, then they also charge you a bunch of other fee like currency conversion fees and transaction fees which is like another 7%, then when you include taxes which is like 20%-30%. That means you're losing about 38%-50% of your revenue before you even get to see any of it. A game making $2,000 a month means its makes a total of $24,000 a year which isn't even enough to pay rent for a tiny studio apartment in most US cities. Then when you factor losing at least 38%, thats only $14,880 a year. Basically no one can survive on that.
Then you have also factor in websites like Patreon constantly screw over their content creators by making dumb censorship rules. Which makes basically job that doesn't even pay enough to even cover rent an even bigger liability. Then add in the potential of someone threatening to sue you is simply enough to sap the motivation out of anyone.
Even without the threat of a lawsuit where you were to make your completely own new intellectual property porn game, the amount of time it takes to develop the game is staggering, and in most cases the skills you learn has no benefit. Because most people don't want put on their resume oh I have lots of experience using Renpy to make porn games, or my only experience in sound and video editing comes from my crowdfunded porn game.
In most cases people simply either learn technical skills from making their porn games then use it as a gateway to learn how to make other stuff that can actually get them hired a normal job, or they simply get burned out, or realize that making self published indie porn games is simply just not a stable or reliable method of income.
