I'm not sure this is true or even have any evidence to back it up, and I certainly mean no disrespect to anyone that may love fantasy, or even writes fantasy, but to me, fantasy just seems easier to justify. You don't have to explain why vampires or magic exists, the way you might have to explain how a technology exists or how humanity evolved to the point of space travel. I personal think it's much more easy to simply say, magic or supernatural creatures are here and common place.
I often wonder for instance, whats so special about a creature drinking blood? mosquitoes and bats drink blood, and there are many sources of blood besides just people, that is the inconsistency of vampires. There is very little difference protein-wise between human blood and animal blood, the reason why there are vampires is that vampires for some reason not explained go after human blood, and it is that act of going after human blood that brings them into conflict with humans, but its much easier to drink animal blood. No one really cares if you raise a herd of cattle to drink their blood. To me vampires are just dumb if examined scientifically.