To the best of my (limited) knowledge, a huge chunk of the m/m original slash writers came out of slash fandom communities and many still belong to them. (I do!) Also, at least some of us are queer; I'm 90% lesbian and am married to another woman. The three m/m original writers I have some personal acquaintance with are all queer, representing a colorful assortment of genders and sexualities, as are some (most?) of the professionals at my publisher.

I don't think anyone really knows what's going on demographically with the original slash community. I don't think anyone has checked. Instead, somebody, somewhere got a notion about heteronormative writers some time ago based on a couple of audible individuals and groups and has been running hard with it ever since. And there's been no rush to correct the errors for one reason or another. The fact that the genre's writers are still fighting to be allowed to join the romance writer's association might be a relevant example of a reason; there's been different battles going on up until now.

The resulting feeling is odd, kind of like being back in the seventies when everyone was making assorted assumptions about my sexuality except for me. I'll admit to having spent a lot of time being annoyed recently...