I mean, I think it's just fetishizing jealousy, which a lot of people(including women for that matter, see the whole cuckqueaning* thing that doesn't get discussed as much), get something out of. It's not my thing, at least not on the submissive side, but I'm not going to judge anyone who has that kink, especially given some of the stuff I'm into. Throw in the humiliation aspect, which again, lots of people like that.
With that said, I'll join in the discussion that came after your post that really wishes we had better tags here. Heck, I think there's a whole third NTR term I can't remember the name of that's like softer than netorare? Don't quote me on that, I just bring it up to illustrate that the word netorare(and cheating for that matter), has to cover way, WAY too much ground.
*So, pertinent to the thread, I want to say Insight of You provides an example of netori with a woman kind of stealing another woman's man... but it doesn't get that far, so I'm not sure if it counts. Female protagonist netori would actually be interesting to provide recommendations for, if anyone has any ideas there.