Same reason guys like lesbian porn. That said as a man who who can appreciate the aesthetic value of a good penis (read: faggot) it's because a lot of women thanks to the media and their femmeboy friends seem to be laboring under the delusion that gay men aren't men. You know how a lot of teenage virgin losers fantasize about a gamer girl who sucks their dick in between fortnite sessions and crap like that? Same kind of bullshit but from a female perspective. They think gay guys are all like a male galpal or something. Gay men are sensitive, progressive, little angels, with wonderful hair who dress well and totally remember their birthday and whatever the fuck.
I noticed this, gay smut aimed at women always portrays gay people as just the sweetest, most innocent, kind, and loving people imaginable.
Meanwhile here in the real world if you make a grindr account I can promise you you'll get 30 unsolicited dick picks within an hour from greasy weirdos who want you to call them daddy and think asking if you're willing to be a "cum slave" within 2 replies is the height of eroticism. When gay men talk to their women friends they're not talking to them the same way they are talking to men. Men in general do this with women, but it's really obvious with gay guys. If gay men usually have a lot of women friends it's not because they're really more "womanly" where it counts, it's because women are just generally more accepting of guys who like getting fucked in the ass. When they're not around though? It's boys night, baby. And boys night don't give a fuck about your birthday. Like, I've noticed this, it's hard to find normal gay porn. Maybe that's a weird statement, but really just go look at any gay porn site. It's generally not well groomed shy boys cuddling and making googly eyes at each other. It's guys in jock straps (always jock straps, why?) railing each other in the ass and screaming "YOU LIKE THAT SLUT?! YOU FUCKING LIKE THAT DICK YOU FUCKING WHORE!?". And I'm a faggot, remember? I like a shyboy! But nope, none of them on there. Pure beef, top to bottom. Ain't no pillow talk in gay porn, woman. If you think straight porn revolves around objectification and fucked up power dynamics go check out some gay shit. Nobody's fucking shy about that crap.
Male sexuality is an aggressive, filthy, thing. You'd think women would be more acquainted with this reality but hey I can't fault them for having a fantasy, I guess.