Noticed that as well, there are some really good male yuri mangakas, but I can't recall any atm.
Aren't Fujieda Miyabi and Minamoto Hisanari dudes? And I know a lot of porny yuri is done by males, like Kurogane Ken and Asagi Ryuu.
Cloud Palette (kinda surprised me, took a look at his other works not translated, some Touhou Sanae het and Mari x Ali futa <- guess thats where Sweet Little Smiles came from xD... and some more nice NSFW for them)
I suppose. I've seen suggestions that feminism is at least partly to blame, since traditional marriage in Japan is actually a pretty crap deal for the women involved, and when they're given the choice they tend to choose against it.