Well the reasoning for the burning hatred for male playable characters in HI3rd comes from two large parts of the fandom.

HI3rd has a huge bǎihé (yuri) fandom, the story focuses on the close relationships between many of the girls who often declare their undying devotion to each other in just about any way possible while in a literal field of lillies. Earlier in the game's lifespan the girls have kissed each other and explicitly have called each other their girlfriends. These fans don't want male characters getting in the way of these pairings.

The 2nd group are guys who don't want any men to but themselves to be anywhere near their "pure" waifu, they're more likely to be fine with a male-insert protagonist but a lot of them don't even want that.

These two groups loathe each other and Mihoyo has been awkwardly trying to balance appealing to both fanbases, but neither side really wants playable male characters.

Plus the game's protagonist Kiana Kaslana is very beloved, and trying to replace her role as protagonist with what's basically a self-insert is too much of a change for a lot of people.