Where all forms of vampire fiction are concerned, the appeal to a female audience is, as LW points out, undeniable. It can additionally be well argued that vampires are far more attractive to females than they are to males and, hence, the reason why such fictions tend to focus more on its inherent female audience. "Twilight" is only the latest fiction phenomenon to exemplify this fact.
So... what of history? What of the historical origins that far predate all such vampire literature and movies? Do they likewise tend to focus primarily on vampires as also being male? In fact, they most certainly do.
From the first written mention of a "vampire" in 1047 CE (when "Father Vampire Insatiable" first wrote down his name thusly), most vampires were recorded to have been male. Additionally, far predating the accounts of such vampires being blood-drinkers, they were instead far more known for their "insatiable sexuality."
As I have documented quite extensively at my own VR profile, all throughout Central and Eastern Europe the vampire "attacked" females not to drink their blood but instead to have sex with them to the extent that such females eventually became "exhausted and emaciated" from their apparently quite active participation with the "vampire" in such apparent long-lasting multiorgasmic sexual congress. And it was this that had such female "victims" resemble those suffering from the "plague" of Tuberculosis. And it was this that gave vampires the reputation of being "plague carriers," which reputation they appear to have had long before their later reputation as, again, blood drinkers.
So... if "vampires" were historically and originally most known for possessing "unlimited" or "insatiable" sexuality ... why males? After all, aren't females really the ones most capable of such "insatiable sexuality" (mulitorgasmic capacity)?
The answer here is an unqualified ... YES!
In fact, it can be well argued that only females are naturally capable of true multiorgasmic ability given that they do not have a "down time" that limits their ability to continue on and on no matter how many orgasms they might enjoy. No... this doesn't mean that all females are multiorgasmic. But it does mean that all females have the natural potential for multiple orgasms. Men, on the other hand, are not naturally capable of this. Instead, for a normal man to experience multiple orgasms... he must, instead, learn certain techniques whereby he must stop natural orgasm so as to avoid the normal "down time" that otherwise he would experience after natural orgasm.
So, then... why males? Why aren't most vampires in the historical accounts female if the female is far more sexually capable?
The answer is surprisingly simple and... in fact... solves the entire question of the historical vampire at the same time: since ancient times, females' "insatiable" sexual capacity has been well documented in all cultures. From the Bible to far more ancient texts, men have portrayed women often as being sexually "insatiable." This was not anything surprising. Thus, no point at all in attempting to portray women as some preternatural or supernatural being for possessing that which was so common the world over.
However... were a small group of males encountered who so uncharacteristically possessed the same insatiable sexuality that equaled that of the female... such males would, indeed, have seemed quite literally preternatural (beyond normal). And, thus, they would have been viewed as being very strange and very suspect.
From this, it was only a small step that began the process of systemic viliification and demonization that resulted ultimately in portraying such a unique race of males as being ... evil.
This explains fully why and how the "vampire" (insatiable feaster) came to be... and why they were all originally male.
What further indicates this as the true origin of the "Vampire" is the fact that females were at about the same time also being very similarly demonized in Western Europe for the VERY SAME THING ("All witchcraft comes from carnal lust, which is in women insatiable -- Malleus Maleficarum [The Witch's Hammer]).
Thus... in those times... women who were sexually insatiable were demonized as witches. And those extremely rare men who were likewise sexually insatiable (a far RARER capacity) were even more demonized as being something far more supernatural: "Vampires."
- Upir'
