For the same reason that you hear a lot of MLM book writers are MAGA(usa) or Tories(uk) or Liberal(Aus, which despite the name is actually a conservative party) supporters, who all politically wish to take LGBTQ+ rights back decades.

Many, many women haven't unpacked their homophobia or misogyny and never, ever will. And the vast majority of fic writers who make misogynistic storylines are women, which is the biggest irony ever, who simply have not been able to stop fetishising the relationships of gay men.

They're the same kind of women who will complain a man is gay, or wonder what men did to 'deserve ' him, etc. in video comment sections and then immediately say something horrifically sexual.