Yes, I know many straight women who find GM horny as hell for them. One explained that for her, it was reading (and writing) about otherwise macho men getting emotional about other men. And strangely, some mothering instinct kicking in, men being vulnerable. Surprised me too, at the time, but live and learn.
From my perspective, I think straight women enjoy writing gay male erotica because we can often relate to the sexual/emotional urges and longing experienced by gay men in regards to their sexual partners. After all, gay men and woman often are attracted to the same physical aesthetic when it comes to men. So, it's not that far-fetched to find the MM sexual/emotional dynamic is an erotic draw for some straight women.
Further, writing from the perspective of a gay man frees women to explore a certain amount of sexual freedom that is often repressed due to the gender roles perpetuated by misogynistic social mores and/or the stigma applied to women who express overly assertive or atypical sexual behavior.