The term itself is a catch-all for three (iirc) different genres/kinks.
NTR as far as this site's tag and most people's disgust/dislike of it extends to the cheating & cuckoldry aspects - Netorare. Which we literally have words for, but "the internet" being "the internet", apathy and laziness means go for the easiest option and to hell with context and understanding.
I am not sure, it is the porn culture + interwebz + western habit of revision of all concepts to their understanding. I did some in depth research, japs literally dig into this NTR themes for emotional damage. But if you look at western porn culture, everyone associate themselves as alpha bulls, who are doing the fucking, cucking and cheating so no emotional damage on average western male on this site who is DEFINITELY above 18, swimming in pussy and already has more than couple of REAL harems going on and these people definitely dont own body pillows.
Male profile jap portray in NTR are feeling inferior, weak and not "enough" hence shame and jealousy. Western porn is either too goofy or acting done so bad it doesnt reflect such thing. I mean i tried to look for reluctant cuck and husband doesnt consent or reluctant, theme is either under harmful content or outright not there. In western culture all these feelings translates into anger.
Then again i have been in this theme for 8 years now as swingers and i met many cuckold couples, it doesnt merely exists as NTR level emotion for them because they take pleasure from the act. Single male side of the question is different too, many guys dont get it and usually mistake the concept.
Hence adaptation happens like this. Closest REAL NTR i found so far is from a movie from 90s, i dont remember the title, but basically some guy hijacks a couples car to chase down some other dude. At some point wife in car wants his dick so they tie down the husband and start fucking, dude manages to move and see them start crying and screaming. Later in movie kills himself. That is the closest scene from west i managed to find which qualifies as NTR for me(edit i found the movie, it is "getaway")