It's a good question, actually, even I was thinking that Shu-Dereth is pretty patriarchal. I feel like because the emperor, the Wyrn, is the sole ruler of the empire and he doesn't have a queen or some high ranking female authority in his "court", so to speak, the priesthood is also consequentially male dominated. Also, not meaning to be sexist, but because of women having a slightly more fragile constitution than men biologically, the processes used by the Dakhor monks would be much more difficult to endure for women.