Nah, that's not it. It's the everything sandwich syndrome that this and many other amateur porn games suffer from. What starts as just one, moderately interesting idea for a game soon grows into an overindulgent mess of fetishes stacked upon fetishes, an endless entanglement of incoherent sexy thoughts that, just like a pizza topped with spaghetti and stuffed inside a roasted chicken, is not as appetizing as all these same ingredients enjoyed separately. The devs themselves find their overgrown projects just too much and simply dread the thought of continuing work with something they perhaps once loved doing those 5 years ago but now unconsciously abhor. Yet, they simply cannot wrap it up due to financing model they've adopted, so it becomes this 25+ season of a soap opera that will never end as long as there is at least one new fan who is going to give this old chestnut a raving review.It's usually because of what you mentioned, burnout.
Rarely you'll see a sex game dev here who'll make a short to medium-length game exploring just a couple of kinky scenarios, but deep and well, while providing an interesting gaming challenge instead of just clicking away and choosing the obvious answers. The game that will have a beginning, the middle and an end, even while still being WIP. Seems like most of them want to dethrone de Sade in this absurd pursuit of yet another perversity, however minute and tepid it might be, to be added to the catalogue of tags and the changelog litany. Despite this, the player sooner or later realises they're running in circles, in essence fooling around with either a text-based or a paperdoll-based sexyfied character creator, not that much different than what the guy next door is making.