Well, this just got darker.
As the other comment implies, that’s just the easiest plot to shove porn into. I don’t think that many people are watching it for the plot, it just happens to be there. Like, people aren’t fantasizing about becoming a plumber to fuck women instead of being paid, for example. It’s just a lazy plot because they need to give some reason for the scene.
I think there’s something to be said for how commonly these fantasies and plots feature specifically young or youthful stereotypes. I think there’s no denying that people are into that sort of thing.
As far as I can tell, humanity has been attracted to young adulthood since at least the beginning of recorded history. I won’t know why we’re still pretending this is some strange or weird thing.
For sure some people are into it. I know from my experience I don’t care for that plot. I still watch them because that’s 90% of porn now it seems, but I don’t pretend like it’s a teenager and a parent involved.
I don’t mean just the “stepsister” stuff but overall the fascination with schoolgirls, babysitters and all that stuff.