Exactly. The moment a male npc gets too close to any npc of the female gender, people scream "NTR", even if this woman isn't planned to be fuckable at all. It's like players expect the MC to be a pokémon trainer who has to fuck them all, but doesn't want any other trainer to have any pokémon.
I do get it. IRL a LOT of heavy porn consumers are romantically unsuccessful. They don't just dislike competition, they FEAR it. Speaking for myself, I'm okay with romantic competition or non romance option girls (or even romancable ones) getting with other male characters. I don't enjoy and almost never partake in 'real' NTR, which is based on arousal from humiliation and jealousy, but at the same time, my tolerance for other romantic stories scales directly with the quality of the AVN. Because Devs have no real spare budget or time to develop side characters or plots, most 'stories' really are pokemon, gotta catch 'em all stories. You move from one girl to the next until you get them all and the story ends. This incredibly unrealistic, but it doesn't matter THAT much. Most AVNs don't have enough quality or story to be anything other than a shallow masturbatory aid. And that's fine, if your story knows what it is and does it well, that's wonderful. Some of my favorite and IMO best porns I've seen here including; Once in a Lifetime, Summertime Saga, Sisterly Lust, Love and Sex, etc.
It's not that these are BAD AVNs, far from it, it's just that if you took the porn out of them, no one would play them.
Contrast this with some other works, such as Being a Dik, What a Legend, Where the Heart is or whatever. These games people have expressed an genuine interest in the characters and story. It's not coincidence that they all have rather high production values and some of them take a pseudo realistic
tone. There are games that lean into the idea that
maybe this could all happen in real life or at least you could watch this story in a movie theater, then there are games that are little more than a cheap vehicle for raunchy sex scenes. Again, this isn't
bad. Porn that is efficient in its goal (to arouse the viewer) is efficient at worse and effective at best, it's doing what its supposed to do. But for anyone whose fetish isn't watching someone else get fucked instead of the self insert character, its counter productive and possibly a waste of limited resources. In that case, its kind of right for customers (assuming you pay for the AVN in question) to be upset, they aren't getting what their money paid for.
So for stories where you are only deriving any enjoyment from the filthy sex scenes, it makes sense you wouldn't want to not just be aroused, but to have Dev time and money spent on those scenes INSTEAD of ones that will.