Yeah it's pretty gut wrenching. Funnily enough the author is making fun of you and calling you a cuck the entire time you're on that route too lol.
from what I have read it's for the same reason people like femdom, humiliation , bdsm and so on it have to do weakness and not having control over your self and this means that NTR to the ultimate symbol of weakness seeing your wife/gf taken by someone else
Personally I like NTR if I'm the one doing it to someone I hate, it feels like the ultimate power move