Problem #1 is the expectations devs have with these games. During the pandemic, people were throwing shit tons of money at these games for a couple of years (wouldn't you know it, everyone being told to stay home and avoid other humans led to increased porn consumption. Shocking!) Some of the devs were pulling in huge amounts, and everyone got it into their head that they are entitled to make 6 figures from developing a porn novel on the side.
Despite what they would have you believe, I do not buy for a second that 99% of these devs are legitimately working on these games full time. Nor do they commonly have years of professional education and many years of experience in game development and design. They should not have this expectation that it will be a full income, unless they actually form a studio out of it and have multiple successful games under their belt.
Honestly, there are a lot of indie game devs who would be fucking stoked to hit 500/mo in reliable income from one of their early games. At 1, 2, 3 thousand a month... they would be straight up crying tears of joy. And those are games that have actual gameplay, mechanics, complex code, and take months to years of development effort before a single dollar gets earned.
Porn game creators are just extremely greedy. They expect a massive return quickly, from part-time work with virtually zero up-front investment. Don't forget, to all those people crying about how we are all freeloaders here... guess what the devs are too, they are all using a bunch of pirated shit like Honey Select to make these fuckin games in the first place!