Enlight me please... How would you make game where 2 main characters are females without any NTR? They would have sex with their boyfriends whole game? Or how that would work?
I think they are more worried about NTR with the male character(s)'s Love Interests.
The whole NTR thing gets really weird when you talk about multiple MC's, especially when they are of mixed genders.
As Male protag games tend to play very differently then female protag games and tend to attract a different/sometimes conflicting audience. From dude circling up behind the male mc and wanting to see him mack on as many pretty girls as possible and keep them all for himself - To dudes circling up behind the female MC and wanting to see how fast they can debase her and turn her into the town bike. Each fan base has very different motivations even if they are both technically doing the same thing.
Not saying it cant work with making both bases happy (like having the female protag be able to choose who she sleeps with, and if stories interact, choosing that person to be the male MC as one of many possible solutions), just that there is going to be tension between player bases.
This is also an issue with people wanting to just pick their 1 MC to play the game through. A lot of people want their 1 person they can rally behind and live vicariously through and don't want to have that person's love interests cheat on them. So having a game with multiple protags is hard unless you can choose to not play the others.