Yeah it's really not a conspiracy theory. And models simply get reused all the time. I have seen the same model not even slightly changed used a in a few games.
I wouldn't resfuse to play to play a game not made with renpy. It is just most games that I play are made with renpy and the engine seems to be the trusted standard.
I would like them to have them. However, AAA studios have more pressing concerns, such as creating a quality game, rather than focusing on enhancing sex scenes. Additionally, including such scenes will increase the game's rating, which many developers prefer to avoid.
It’s frustrating, especially when the devs seem active but then suddenly disappear. I suspect some devs make enough money and decide to stop. Others might simply get burnt out and choose to drop their projects. Meanwhile, some abandon very promising projects only to start new a one that racks in...
As a lurker I don't have too much of a problem with it. But with it's mods I feel selective enforcement of their rules. And the drama that comes with removing a game for breaking a rule but not another that does it.