I am a male that usually plays as a female. I have many reasons.
One reason is I am a male that was raised by women, I never had a male in my life growing up, I had a mother, I had an Aunt and I had a Grandmother. As a result I turned out to be rather feminine.
Second reason is I was bullied a lot in highschool, bullied by boys. I grew up with mostly female friends. That's not to say I didn't have male friends and that I dislike males though.
Third reason is I am built very slender and I look rather girly for a male, so playing as a male with big muscles doesn't really suite me sometimes, unless I want to be something different.
Fourth and most important reason. The people I looked up to most in life, whether they were singers, actors, role models, what have you. Were all female. So playing as a female makes sense to me.
My two favorite types of characters I like to create in RPG's are Feminine males, or Tomboy females. Gender just really isn't that all important to me, if I can shoot fire balls out of my hands, why can't I play as a girl?