We just have different frameworks.
To us guys that dislike NTR/NTS, it's hard to fathom a dude wanting to share his girlfriend or wife.
If he wants to share his girl with us fine, we'll take it if we're hungry, but he better not be hanging out in the corner, and GTFO.
Of course that scenario is only in-game. In real life I wouldn't want another dude's chick, even if they offered.
Game-wise, just the thought of NTR is gross, but being the bull doesn't bother me.
I'm not a harem guy, but I do get the appeal. I do have that darker impulse.
But I disagree with it on a moral and practical level, so I cannot embrace it.
I have no such dark impulse for NTR/NTS that needs to be fed though.
So sharing in a game is not NTR to someone that has that impulse.
It's like, high-five, we're buds, let's swap. High-five bro.
To us non-NTR dudes, it's not a high-five, but a punch to the face.

To a guy that hates NTR, any other dude inserting his penis into their girl is NTR.
Harem vs NTR, is like a Territorial Barbarian Warrior framework vs. a Free Love Hippie framework.
They just won't mesh.
Mastering the Pink Box is not just a Free Love Hippie framework, it goes beyond that in depravity.
It's more of a corruption/use and be used game. No allusions to love involved.