Some people are ultra-purist about it, and don't want their girls doing anything with anyone else, even other girls (whether in the harem or not).
There are two or three sides to this. First, just not everyone is a big fan of seeing two or three or more women having sex together like. These people will not be impressed nor turned off by lesbian scenes per se, but not excited to have a lot of them in game either and may well move on to next game if first three or 4 scenes are lesbian, mom/dad and woman / BF whether that is NTR or not and MC has no action beyond fapping voyeur.
Second it can be of course be NTR if all other criteria are met and else sharing or even cuckold/cheating depending on setup , well see first for sharing and NTR has its own drawbacks even if many seem to have less problems if the one doing the NTR is female.
Third and often my biggest problem with lesbian sex in male MC games is that the lesbian sex or even the females take over the game (This is also often a problem with NTR focused games that offer avoidable paths that setup and making NTR possible with chars or having to constantly stop it takes over the game), we have after all mostly only one male MC and 5-6 or more females. Same if in this game you would show all lesbian scenes of the older daughter that also has a big role with MC and shared scenes she would likely completely take the game over and it be more or less all about her scenes and a corresponding problem is that you show things that MC is not present for which can also hurt the male MC perspective of the game. Which last is great if you like scenes of her(as a dev though making a female MC game might have worked better in that case
), but if want scenes of MC with all the girls or another as her less great.
