Manipulation and blackmail is the basis of BB incest (75%).
Kira - voluntarily.
Anna - the manipulation and use of Anna's disease.
Lisa - manipulation.
Alice - manipulation and blackmail.
And in the BB remake - Glamor, Max has no reason for incest. There is only his desire (desire DS).
In the remake of BB - Eric's glamor will not. There will be no need for incest. DS wants to do a BB remake - a game with incest, as originally planned.
DS likes incest, so he makes an incest based game.
(sorry for the inaccuracy: he does a BB remake)
If he had made Glamor a full-fledged game, and not part of a remake for BB, I would not care.
I'd argue that in the case of Kira it was her manipulating Max for incest, although he was definitely willing. She wanted his help to jumpstart her porn directing career and for her to finally obtain her goal of being with Anne. But I'll also admit this might just be me reading too much into the situation.
I'd say that DS wanted to make an incest game because incest was popular and a way to make money, but he has little to no interest in incest himself, and as I've said before, he's openly said that he doesn't really understand the appeal of incest. I've heard that incest won't even be acknowledged in Glamour when the BB stuff is added. I'm hoping that this is just making a nod to Patreon's rules, and that there will be a patch or mod. But I could honestly see DS just adding the characters back into the game, calling them roommates, and not taking it any further than that, which I think would be a colossal misfire.