You dont play enough nts if you think cuckquean is common. Thats just not flat not true.
And not cause i wanna start an ntr debate but most of them, the corruption doesnt even make sense, rushed and instead of corruption the girls are typically just whores from the start. Hard to feel tension when they were corrupt from the start. Very few actually have real corruption. In this way ntr is really just as vanilla as everything else you described. Big dick shows up, girls gobble it, end of story. Just as mega chad bulls as a harem protagonist. Its all the same shit, some people just want a novel in their visual novel.