Vampires were originally a personification of the fear of disease and infection.
I still haven’t figured how they became romantic, undead demigods. Even Dracula was pretty repulsive if you read the actual book.
It started because a few adapters of the Dracula story decided there should be a romantic link between Mina and Dracula, some even built that link on Mina resembling Drac’s long lost love from his human days. Then Ann Rice (and a few others, the creators of Forever Knight come to mind) comes along and thinks this “forever love” thing is cool and runs right off the deep end with it, along the way they realize vampires don’t age, and of course “forbidden creature of the night” has so many superficial similarities to your basic “bad boy” romantic figure. And walla, vamps are romantic undead demigods.