One, that leads to a total route loss and a bad ending.
Two, IIRC Cari got so much flak from that that he promised not to add something like that ever again in his games moving forward.
Three...I don't even know if there's anyone in the game who could serve as an NTR antagonist. Axel? He pretty much promises to destroy you and the people you love because he thinks you offed Benjie (I mean you could argue that he could hire some goons to rape the girls in front of you, but I don't think he has that kind of influence or power). Thanatos? He's pretty much driven into finding the Gems of Doom and hardly spares any second thought on anything else (hell, he even outright ignored Orion when he stood up to him in Ekabar...and that's likely more to do with the latter not having a gem in his possession so the former just treated him as a nonperson). The Founder? Pretty much the same as Thanatos I think. Raul and Noah? Naaaah, they're more mercenaries and gag material. Plus they're cool with Orion. Kai? Eh, completely harmless unless you do absolutely nothing with him and Nancy. Jerry?
/tries his best not to laugh at the thought
...yeah, not happening.
Chang?
/looks at him and Mikaela
...yeah, ABSOLUTELY not happening.