Who needs to drink... wine?
Alright, I've got it.
Vampires have a condition that causes their cells to perform anaerobic respiration differently. Instead of producing lactic acid like the rest of us, their bodies are frequently being pumped full of waste alcohol.
In order to survive, it's absolutely necessary that they continually dilute their circulatory systems with fresh blood, to keep their BAC percentage down below lethal levels.
is why you've never seen a vampire driving a car.