I've been thinking about the steady increase of porno involving siblings, parents, or some sort of parental substitute (sexy teacher, lascivious nanny, etc). I'm convinced that this is the result of further atomization under capitalism. As social relations and active participation in community continue to degrade, essentially the only people you will have any sort of meaningful connection to will be your immediate family.
If you're lucky you picked up some friends at school and got along well with your co-workers, but it's very likely that you have no emotional ties or experienced any sort of physicality with anybody outside of who you grew up with. Of course you're going to end up horny for Daddy when everyone outside of the nuclear family is basically an alien that you're incapable of feeling any sort of connection to.
Somebody's probably thought about this more than I have, but I don't feel like I'm off-base in saying that incest increases in popularity as everyone's social circles continue to contract. Or maybe Freud was right and people have always wanted to fuck their moms, I don't know.
Honestly this is pretty woke. My most terminally online friend is the one who is particularly into incest. Of course there's also the question of whether or not this is just the same reason we have more left-handed people and homosexuals. Kink is in general becoming more accepted, and stuff like stepsiblings and 'mommy' stuff might just be more widely recognized purely because increased visibility, rather than a rise of capitalist alienation. So it might not be that 'sexual deviance' is on the rise, it's just becoming better known and less repressed.