Ntr can be interesting, just like any other kink. It isn't interesting because almost every ntr story is the exact same copy paste. Same braindead females, same retarded blackmail plans that make no sense, same blind, deaf and socially maladjusted husbands/boyfriends, who can't see their partner literally bouncing on another dick in front of them. Same scenes, progression, ending. And especially in games, it makes them practically kinetic novels. You just get to choose if you want to see the slut getting fucked while on the phone or behind the closed door.
Ntr practically means cheating/romantic betrayal and humans have been writing interesting stories with that element for millennia. Illiad had ntr in it. It's the obsession with the exact same tired tropes from the japanese stories that makes it boring.