I personally don't think the "most women like men, duh" argument holds much water. As has been pointed out, shipping is not orientation, and plenty of lesbians like m/m. I've also met plenty of straight women who love f/f, who if you give them a chance will rhapsodize about it more than most lesbians. A popular reason for straight women to like f/f is the focus on female pleasure and female sexual response. Even het can sometimes get too focused on the male character's penis and orgasm. You also get more descriptions of varied sexual acts, e.g. breastplay, that are rare in het. Or they might simply get into a fandom where they think two female characters have great chemistry!

Hello, that would be me and the Expanse (Bobbie/Chrisjen, Drummer/Naomi) and a whole ton of pairings on Dark Matter and 12 Monkeys.

It actually took me a long time to get into slash as a bb straight fan because I felt so excluded, as a woman, but now I do find MM slash hot. But I'm also happy I started reading slash mainly after the "now he realized why he had always felt so unfulfilled kissing a woman (unflattering details)" stage, because I have enough gender/body dysphoria all on my own, thanks. (I do still see some misogyny like that in particular fics, but it seems to have fallen out of favour as a general thing.)