I kind of agree here. I think where this one failed, as far as being an NTR game goes, is the setup. None of the girls have anything to do with the mc, iirc. Just 3 dudes picking up chicks on the beach. That can't really be construed as NTR in the slightest unless you're some kind of delusional narcissist who thinks every girl in existence is automatically yours lol. A big difference between this and Sana was that Sana was your wife iirc. There was a lot more investment in her being stolen in that case.
If breast mafia had instead created a scenario of characters close to the mc in some way, it would have sold the ntr a hell of a lot more. Basic things like say a childhood friend with a crush, a caring mother who suddenly loses interest, a brother complex/naive sister who has that used against her, a girlfriend/fiancee/wife, etc. Just a few standard ones off the top of my head.