I don't think I can eloquently explain why so that you could understand it. I don't think I fully understand why myself.
The sweet, cute/innocent girls are like the ones you want to hold. They're ones that you want to protect if that makes any sense. I can't explain what it is about them that makes you feel that way other than that they are sweet and innocent (they have to be that way and not just look that way too in my case).
giiiiirl, there is a very VERY long history of men highly valuing purity in women (read: innocence) it stems from before the bible and is thought to have to do with men being intimidated by female sexuality and therefore wanting control it while simultaneously profiting from it (like colonizing land). its too complex to break it down here but there you have the short answer.