I'll get ahead of you and intelligibly explain "what and why". The answer to QuEsTiOn is that I, like any other sane person, won't take seriously attempt of being lectured (Yep, its clear what you tried to pull right here to anyone who answers with expected by you answer) by some random from the internet on account of MC being a fuckboy and having a lot of girls, as a decent reason for those same girls to fuck around too, lol) I'm not ashamed (nor should I be) for liking power fantasies about harems with great loyal waifus or smth like that. What a dumb thing you tried to pull out here in hopes of shaming or proving wrong people for disliking Dev's dumb and displeasing game decisions, by making one of the characters from another his game a cheating, deceiving whore. Don't forget, if you, personally eat just anything on the plate, it doesn't change the fact that other people actually have preferences, tastes, and strong opinions about things
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No wonder you like and eat everything he makes without any questions
My ex herself played on the phone in a lot of dumb dating sims for girls about harems full of tall, six-pack, mysterious vampires who loved and worshipped female player without any reason and with absolute loyalty) And I didn't mind or lectured her about liking such games with these fantasies as long as they were only fantasies for self-enjoyment and didn't influence her perception of reality. I'm pretty sure that she'd understandably be frustrated/disappointed too if, for example, in the new update in one of her games, out of nowhere, one of her "boys" cheated on her character with some other female just because)
P.S. I don't care about exactly this game, its characters, etc. I just answered in general to your question about why exactly people don't like the bullshit decision that Dev made with the character.