The vampires lust in of itself is sexy by nature, while their lust is indeed a bloodlust, their evolution has lead them quite naturally to have an exterior that attracts the kind of mate they lust for which is a victim rather than a lover. Thus they have pheromones, soft tender skin, curves on the vampress, chisled features on the vampires and their scent is something wholly desireable to the human nasal sensory organ in order to lure us in.
If they were repulsive we would be more difficult to pray upon and would band together to destroy them during their weakest moments. There is also something to be noted about the typical uptight Victorian repression in the manner of most forms of dress for classical and neo classical vampires which is we often do things that are taboo... or desire what we can not have. It is instinctual.
It is also instinctual for us as humans to venture into danger, a primeval instinct that often gets us into trouble as flirting with Danger can ruin or Even end our lives...
Plus it feels good to get your neck sucked now and again