Please don't acknowledge the obvious trolls regarding (if this were a male, durr durr durr).
My preference for female/female stories has to do with the fact that I'm a lesbian and I LOVE WOMEN WHO LOVE WOMEN. I will literally go out of my way to read/watch anything with lesbians. And I get that's a bias, so what? Not your problem.
(Now trolls who want male/female, go away and read the one billion other choices there are in the world of heterosexual life).