"People don't like this game simply because there are vanilla scenes in this game" is really really bad excuse if you are trying to defend this game or shill for the dev.
One of NTRman best rated game has vanilla paths. No one ever complained about that.
The reason why this game is not getting as highly rated is the same issue from his recent Lust Voyage game. The WRITING.
Why do people enjoy his past game so much? Because there are always good build up, good premises, difficult moral dilemma, slow burn, mystery, double pov type of NTR going on. We got to see how the MC become more and more helpless, the situation getting more and more out of control, and the female character will inevitable fall into debauchery. That is the type of NTR story people are expecting, and dev used to deliver it, whether in his past comics or games.
This game on the contrary, is just too blatant and too direct, with the whole set up being exposed in less than 3 minutes of opening dialogue, MC and wife just simply say yes, and game even deliberately throw a "defeat on purpose" button so you could just skip to the scene and voila, the wife is now getting fucked by other men.
That is some of the most lazy and un-arousal way to write NTR story. Much like a novice writer would do.
The wasted potential is huge here. It could have been, for example, that the MC is trying his best to win the challenges to avoid getting cucked, while the wife secretly provide sex service each night to the tribesmen so they go easy on the MC in the challenge. (with some suspecting from mc and some mystery pov like usual) So while MC thinks he is protecting his wife, she is already falling deeper and deeper into lust and in the final moment it gets revealed with her getting gang-bang in front of husband or something. That would be much much hotter than the current version of story.
I have nothing to complain about the art or the (albeit simplistic and really old school) gameplay. But the writing. All I can say is wasted potential.