It's been mentioned before, but there is no reason to have this trope be named "Netorare Genre" when it not only does not apply to Japanese-only media, but actually redirects from Cuckold anyway.
Renaming it Cuckold will allow us to include other examples that have nothing to do with genre, either. Such as the Futurama movie were Labarbara leaves Hermes for Barbados Slim, and whom Hermes dreadfully discovers is a superior man to him in every way.
Calling it "Cuckold Fetish" would, in my opinion, remove the possibility of using non-fetishistic examples of the trope. The Futurama example above is one. It completely fits the "Cuckold" archetype, but it's not played explicitly for fetish.
Frankly I don't see any evidence that this is broken. Also, the huge number of inbounds compared to the relatively small number of wicks suggest to me that lots of people are coming here specifically to learn about this term.
Also, If we were to have a page for "Anytime anyone sleeps with someone else's significant other" it would not be this trope. It might be supertrope to this trope, but it should not replace it.
[upThat's a minimalistic version of what "cuckold" means in a fictional context. It's not just a spouse sleeping with someone else, but it's an up-play of the conflict, discomfort, humiliation and betrayal that comes from it. How much it's played is dependent on a sliding scale.
That said, maybe naming it "Cuckold" would lead to misuse. But the "Genre" part should be dropped nonetheless.
I'd venture to guess that this is because English speakers don't have much reason to use a Japanese word unless they're talking about the genre.
The word itself is just a particular conjugation of the Japanese verb "netoru".