I know the pain. There's just not that many games like this. Always one or the other. I tried making a game to cover that space, but pivoted into writing very early and left the project. It's rather sad that most devs are kind of vanilla with their games, or it might be an audience thing, to not scare them off. IDK
Well there is a joke running in f95 i.e. "Mom is the ultimate prize and only be fucked after all the rest of female characters". Not only for mom, but sometimes this theory applies for sis too. The point is, Devs dont want to go beyond the "safe limit" for these characters especially they are incest and taboo. They say it will be "unrealistic" & "illogical" to go beyond the box.
But I would say that they dont have convincing storylines or dont have that much talent to make incest stories in a way that it can be both convincing and also raunchy and kinky enough too (without using corruption or fantasy elements). So many of the devs dont want to put brains to think out of the box especially in incest games. They still stucked in age old "vanilla" character archetypes because they dont want to risk. They think most of the playerbase likes normal vanilla stuff with great focus at romance conversations. But, thats not true. Our brains are developing day by day to accept the updated characters in our real world too. In olden days, talking about sex is so taboo. But now, it is not that much.
I would say i like Linda in Milfy City. Because, unlike lot of other incest games's Moms, she is the one who chase the Son first & convince Son into incestual relationship. It is so out of the box especially at that game (because it is happened some years before). Did Linda got hate? No, Linda got the cult status and there is lot of fanbase for that character.
So, what i want to say? Well, whenever there is new invention or discovery, some people will oppose.. But, there will be a time where it will be spread like anything. Examples: invention of cellphones and computers.
So, unless devs gonna take risk and ready to fail sometimes in order to spread the word and give time to the players to get habituated to this stuff, when still see the same vanilla incest shit for many upcoming years too.