I don't really think Netorare and Netori should be put together just because they both involve cheating, tbh.
NTR is usually more about emotional intensity than anything else. I've seen a lot of takes online, and what keeps coming up is that people who seek out NTR often approach it from an emotional masochism point of view.
We have a lot of people who are dealing with stuff like depression, loneliness, emotional numbness, or even just a general lack of empathy. So NTR with all its betrayal, jealousy, shame, etc, delivers the emotional hit. Negative emotions are stronger. And for some, it's a way of "feeling something".
It also seems to resonate with people who have control issues or abandonment trauma. It's like watching your worst fear in front of you, which gives this weird sense of catharsis. Like, "How would I feel if my partner was taken from me?". Kinda fucked up, but it scratches a psychological itch.
There's even the idea of role reversal, where people who see themselves as the loser who never gets the girl start fetishizing being rejected. So it becomes the fantasy. Which in a weird way, gives it power.
And then you've got porn conditioning and desensitization, maybe even voyeurism. (And this is just me thinking out loud now) I haven't found much research connecting NTR and porn addiction, but there is research saying that heavy porn use leads to needing more extreme or novel content. So maybe watching strangers have sex over and over could eventually morph into wanting to see your partner with someone else, which might be where Netorase starts to come in.
But Netori is whole different thing, it's more of a power trip. Same as it goes with Harem in a way. It's about domination, conquest, taking what belongs to someone else. Way more ego-driven than NTR, which comes from vulnerability.