>>8707409 (OP)
So we already have theories that it's because the Japanese are cucks. But I'll give an angle that I don't often see in these threads. People also like having drama and adversity in their stories as well as some mystery. NTR is popular because it is about the plot. You don't know if the boyfriend will keep the girl or not. Will he be pathetic? Will he take revenge? There are so many different ways the story can go with this. Vanilla stories you know are going to be guy gets girl, the end.
I watch NTR one of two ways. I either skip the sex scenes to watch the plot, or I skip the plot to watch the sex scenes. Watching it all with context usually sucks.
Some guys say it's for cucks, others say it's for you to self insert as the bull, and some rare few say it's for women to watch. I saw it's for people who like plot twists.
Interestingly, NTR is similar to corruption. The only difference is that NTR involves taking away from someone else. Corruption usually is a magical girl thing that only focuses on breaking the girls spirit. Where NTR breaks the girl's spirit with a consequence of taking her away from her lover. I really like corruption due to my religious upbringing, but I don't like NTR, however I don't whine about it either and I'll watch it if the art is good or if I skim through and the plot is different from most NTR plots. The only thing I really don't like is NTR disguised as vanilla, but thankfully most put NTR in the tags or on the box art.