This is my perspective on why the route should be the way I originally wrote it.
To start with, I understand where you're coming from — because typically, in most sharing-type games, the male or female protagonist initiates a conversation about their fetish, saying that they have a certain kink. Then, you get to choose whether to go for the vanilla, NTR, or sharing route. But from a game design point of view, I think that most players would mainly play the vanilla or NTR routes. Even though most of us in this thread may prefer the NTS or sharing content, from what I’ve observed regarding public reactions to that tag on doujin sites or Facebook pages, it’s generally worse than the reaction to NTR (I don’t know why either). Most people seem to see a male protagonist with that kind of fetish as mentally disturbed. That’s why I believe NTS should be a branching option off the NTR route.
Take NTR Knight, for example — even though it has an NTS tag and most people here like that route, and I do too, I still think it didn’t go far enough. It could have been better in terms of NTS content. But I think the creator probably wanted to keep it in a gray zone. Otherwise, if they intentionally designed an NTS route, it would have had a specific NTS ending and a protagonist who reacts more like the MC in Nebel Geisterjaeger.
Coming from an Asian perspective, we’re still not that open about sexuality. A woman in her teens or twenties openly discussing fetishes — even with her lover — isn’t all that common. (Of course, it’s gotten better these days, but it’s still somewhat taboo.) So in my view, for a woman to be open about this with her partner and agree to go down the NTS route, she’d already need to have an interest in that kind of thing (she’d have to be a bit lewd). If you brought up this kind of fetish with your average Asian girlfriend, I’d say maybe 1 in 100 might accept it. That’s why I wrote the story in such a way that the heroine has to be corrupted to a certain extent before she can enter the NTS route.