- Edited
I don't think it's really been too prevelant here. Certainly not as much as it is in 2D porn, where it's basically become the default. Going completely on wild assumptions more than data, but I think people were initially drawn to stuff like SisLovesMe because it was porn with actual set-up and little mini-episodes that would gradually build up in tension. The fact that it was faux-incest was kind of secondary.
Then studios realized just how quickly and cheaply they could churn this stuff out and it exploded; minimal sets or costumes, you can use the same house over and over. Just say the two people fucking are step-siblings and that's all the set-up you need. People that want the taboo aspect are served. People that don't care about it at all can easily ignore it since the story goes out the window as soon as they start fucking. The tube sites get infested with step-porn and a majority of people clicking don't care and just want to see the hot girl.
Now all of these companies are looking at the data and going "people fucking love incest, let's make more of it" and it becomes a self-fulfilling prophecy.
Personally, it does nothing for me and I can't wait for the next trend to come along and replace it. Any taboo element that could possibly be at play goes out the window when a) the guy's "step-sister" is willing to fuck after a couple minutes of him acting weird and rapey with barely a hint of reluctance and b) it's the 74th step-family scene I've seen that month. If every scene is taboo, none of them are.