>>213019241
Dracula needs the blood to continously renew himself. He's dead and doesn't have his own with regenerating blood cells and whatnot, so he needs to consume fresh blood to keep himself "alive" indefinitely.
And then all other vampires are based off of Dracula. The 'elegant count' version we're all familiar with is a pop-cultural image, and it's no less right or wrong than the more cadaverous version in Nosferatu.