Sci fi has an image problem of being for geeks. Vampires and horror tinged supernatural stuff can be seen as cool.
Funny how superheroes were also for geeks not too long ago and now they're in all the biggest movies. Sci fi needs an image makeover.
I often wonder for instance, whats so special about a creature drinking blood?
Sexual metaphor. As always sex sells, and sci fi tends to be sexless. That no doubt is a big part of the problem. Of course Tolkein was pretty sexless too and I don't read enough fantasy to know whether the puritannical streak endures. GoT is very popular and also raunchy, no coincidence.