Deep down, people are the same. I think, that it's the "strong outsider taking a weak local man's woman", or a "strong savage man taking a woman from a nice, but weak guy". It's always a story about 2 familiar and similar people who are somewhat weak and timid, when some outsider who is completely different in contrast, steps in and takes it all. Both examples share this. And the reason that it's always a japanese black haired "Protagonist-kun" or a "white whimp" is, that those guys seem familiar to us, not exotic as the homewreckers.
Too bad most stories like this are from a perspective of the guy being cucked, because I like to insert myself as a guy who does the stealing.
I wouldn't do it irl, because I wouldn't want to hurt real people, but in a fictional story, I can relate.. it's kind of my savage self deeply buried inside. That's why I like stories like Conan and such.
Damn, taking somebody's wives is even in holy books.
Oh, and I like when an isekai or harem anime protagonist gets cucked, because I hate isekai and harem protagonists.