I'm sure we've seen all the goofy Step-Dad, Step-Mom, etc porn coming from Digital Sin, etc.
I recently saw some anti-porn material using the ubiquity of these titles on tubesites to further attack porn as 'violent' and promoting 'rape.' Ironically many of the scenes with incest titles are just regular gonzo scenes that someone has named with an incest title.
This theme has always been with us, many 70s loops and features like Taboo dealt with it but it went into hibernation during much of the gonzo era.
It has certainly reached the saturation point and many of the scenes are very much half-assed in terms of the scenerio being played out, which is a good thing imo as too much 'Daddy' talk can get creepy.
My guess is that with the downturn in the industry Digital Sin had to find a niche that would boost their sales and found that this worked.
Got to admit the apparent popularity of the titles does surprise me, do you figure these sell better in Southern US?