Not gonna trash talk your kinks. Just saying taboo is a social construct and depending on where you live, sex between unmarried adults may be taboo. I could make you a game set in saudi-arabia, 'dating my neighbour's daughter' and have exactly the same character progression as in DMD and other run of the mill incest game. And also niqab, because dude, why else would i make this game? Yet, It wouldn't tickle me as much.
People will still commit incest if it was legalized because love and affection are what drive people together. trauma (family crashdown), lack of partners (prudes!) may cause 'abnormal' behaviour as a coping mechanism. loss and loneliness may create love. your daughter / sister may chose you after a break up just as probably as 'random encounter 4325'.