Because they're really obvious.
5. Vampires from a devil-horned alien planet with super vampirizing eye lasers.
4. The "half vampire" vampire hunter.
3. Vampires fighting a zombie plague because, well, they need human blood.
2. Vampires attacking a town in the Arctic circle because the town will be in total darkness for a long time.
1. Vampire porn.
(Having read the book, it might be "soft" porn, but yeah, it's porn. I mean, it was written in Victorian England.)