Why do I like girls that are dramatically different than me?

I have quite a few platonic relationships with girls and I can always spend a non romantic day with them and have a blast. I'm very compatible with most of them, can hold a really good conversation with them and be surprised by our many similarities. But the thing is, I don't want to date any of them. To me it would be as if I decided to ask out my favorite cousins. Now the girl I want to date is extremely unlike myself. She listens to current pop hits and post- acts(whatever the hell that is) while I listen to everything under the sun but will avoid hearing a note of what she tends to like. Additionally she's more conservative than I am. I'm a borderline far left hippie and atheist while she's a moderate conservative christian who loves guns (she sleeps with one). Obviously we share few views. But anyway, why is it that the girls that I share almost nothing in common with rule my fantasies while the girls that have a lot in common with me do not? I read about love all the time and what I've read shows I should be into people more like myself. Why am I the exception?