I agree and suspect it's one of 3-4 things.
1. Games written by a dev who likes corruption + cheating-slut scenarios (either being or screwing the cheating slut) and decides to throw the cuck or hotwife path in as one of many. The relationship aspect is an afterthought for them, with the person being cheated on just a prop to fulfill the corruption fetish. I'd put EvaKiss in this category. [Wouldn't dare post this in the ORS thread as I'd get verbally mobbed. But it's clear she's got quite a fetish for BBC + cheating in general, though not so much for the relationship aspect afterwards, based on the quality and slant on that path-turn in GGGB and the now ret-conned/watered-down ORS....
Preemptive: "Yes, yes, yes. They're still great games and she's a fantastic dev. Don't kill me, ect, ect, ect"].
2. Sub devs into heavy fem-dom and/or sissification, with the cheating/cuckolding as one of many humiliating aspects of that. These are the vast majority of this sort of game and the most unrealistic.
3. Cuck/hotwife games written by devs who've had little or no real relationships with women that weren't transactional
OR just aren't very good writers and don't think to analyze what makes writing suspenseful and what makes a scenario hot. Of course, both could apply to the vast majority of games on this site, too.
Though promising at first, I'd chalk A Couple's Duet up to the latter and several other of these games to both.
4. Devs just in it to pull as many kink demographics in as possible, which could also be applied to #1. I don't see this one as common though, since the "NO NTR FUK U BAD DEV IS GAEEE" crowd often takes away from any income gains achieved by including the path when appealing to the largest (read: harem) market.