Women being obsessed with Gay men has been a thing since time immemorial, and exploitable. Think back to Star Trek brought back by Spock/Kirk slash fiction.

Anyway, the easy answer to that question is that historically women love interests don't get written all that well by majority male authors, usually into lame romantic subplots, getting the girl stereotypes, or objectification. Few women want to self insert into a female character that's essentially an afterthought. Writing more elaborate romances slowly building up feelings on equal footing takes too much time as well.

Male on male relationships compromise on that. It's inherently on equal footing that sexist stereotypes don't give as either character can be top/bottom, and also specifically caters to quick lustful attraction that is more snappy and easy to write bout. Established properties tend to treat men as protagonists way more commonly than women, so they have the benefit of already having more personality to work off.

On top of that, gay men often fall into stereotypes that are less threatening (effeminate, twink), more hygienic than stereotypical straight men (more likely to wash their butt from rooted homophobia, less hairy, more clean cut, not fat...), and don't act like they deserve someone, instead gay ships tend to be more about giving into often forbidden carnal temptations.