several reasons. to begin I completely reject the hacky armchair explanations of it being 'vanilla with minimal taboo' as well as 'having mom issues'. we've had a thousand of these threads and I've never seen a single person say they're interested in their IRL mother. it seems to be extremely rare. and the vanilla thing just makes no sense whatsoever.
for most usual scenarios (mom + son mc) it's the reversal of power relation, the conquest of the most unattainable love interests. it's like seducing your teacher on steroids.
how it works for dad mc + daughter I couldn't say, I don't go that way. for me that power relation is the exact opposite of what's hot, the stronger going for the weaker which is just abusive. often the problem is dealt with making the weaker (non-mc) party be the initiator, but that just makes the dad mc insufferably patronizing. I assume the people looking for these scenarios look for something very different from mom + son mc. I'd love to know what, it's always interesting to hear about the kinks you don't have and can't understand.
some look specifically for the abuse and degradation of the 'love' interest. in those cases I'd think the point is having the most sacred or innocently pure heroines to corrupt. if abusing a non-related person does it for you, clearly abusing a family member takes that one step further. this seems very logical.
the asshole big sisters seem to either be about having a 'justifiable' emotional ground to abuse them (the opposide of innocent/sacred heroines), so being a monster wouldn't feel bad. the other case is submissive players looking to be abused by trong and mean heroines. often games mix these two which rarely works. probably never. - maybe should be pointed out that these are power relation reversals as well.
how female protagonist versions of these work are a complete mystery to me. often I see people say they're not identifying with the female mc (even when player herself is female) but with the abusers. but it doesn't make sense to me because then I'd assume they'd be playing games where mc is the abuser. not a helpless victing stumbling from rape to another. but it's probably because I don't have the kink so I can't understand the mental mechanics.
TLDR: most cases seem to hit on role reversals, not a hidden desire to fuck your own relatives.
for most usual scenarios (mom + son mc) it's the reversal of power relation, the conquest of the most unattainable love interests. it's like seducing your teacher on steroids.
how it works for dad mc + daughter I couldn't say, I don't go that way. for me that power relation is the exact opposite of what's hot, the stronger going for the weaker which is just abusive. often the problem is dealt with making the weaker (non-mc) party be the initiator, but that just makes the dad mc insufferably patronizing. I assume the people looking for these scenarios look for something very different from mom + son mc. I'd love to know what, it's always interesting to hear about the kinks you don't have and can't understand.
some look specifically for the abuse and degradation of the 'love' interest. in those cases I'd think the point is having the most sacred or innocently pure heroines to corrupt. if abusing a non-related person does it for you, clearly abusing a family member takes that one step further. this seems very logical.
the asshole big sisters seem to either be about having a 'justifiable' emotional ground to abuse them (the opposide of innocent/sacred heroines), so being a monster wouldn't feel bad. the other case is submissive players looking to be abused by trong and mean heroines. often games mix these two which rarely works. probably never. - maybe should be pointed out that these are power relation reversals as well.
how female protagonist versions of these work are a complete mystery to me. often I see people say they're not identifying with the female mc (even when player herself is female) but with the abusers. but it doesn't make sense to me because then I'd assume they'd be playing games where mc is the abuser. not a helpless victing stumbling from rape to another. but it's probably because I don't have the kink so I can't understand the mental mechanics.
TLDR: most cases seem to hit on role reversals, not a hidden desire to fuck your own relatives.