1. We love an impossible love story. A vampire-human relationship is about as impossible as they come. A vampire drama has enough UST to keep us watching for 7 seasons.
2. Longing for ... what? We all know this angst. Vampire dramas capture it so well.
3. We love superhero stories but feel silly watching them as adults. Good vampires are superheroes without the fancy dress.
4. We love a fight scene. Gun fights are over so fast and there's too much blood. Vampires and demons fight with their fists and cool wooden stakes. Afterwards, there's no messy corpse to deal with - just dust on the floor.
5. Once vampires are accepted as reasonable, the door is open for demon characters, witches, mind readers etc. So many possibilities.