I like girls. I like how they look, I like the way they sound, I LOVE their fashion options. It isn't really any deeper than that. That said, I'll usually always play a male character in a Souls title, because [insert valid reason for inconsistency here.]
EDIT: I guess if I had to further expand on this, I'd say that female characters give me a way to explore options I don't have as a tall, bearded, broad, 'built' man. I've always loved cuteness, hyperfeminine fashion, "girly stuff", and so in addition to just really, really liking girls, video games allow me to explore the cute, feminine avenues I can't in the real world.
Also, as another commenter stated, I'd also just rather look at a girl's ass than a guy's for the entirety of a playthrough lmao