Zombies have no real mythos or history. Most zombie stories are merely metaphors for issues that at the time can't be discussed head on due to the popular opinion of the time. George Romero's Living Dead movies are prime example of that. His movies really weren't about the living dead but more to do about messages concerning racism to consumerism. Only after the success of those movies, did zombies become popular in our culture and zombie movies were made just for the sake of making a zombie movie. But that means if such movies are based on these metaphor movies, then in a way they're echoing the original message, even if they don't intentional mean to do so.
I do realize that Zombies do have mythos of their own, but most of their history now is based in more current pop culture than original black magic myths of Vodoo and Ghouls that originally spawned the term. You could say that the current zombie is a modern invention so of course reflects more modern viewpoints (which typically are more complex that historical superstitions which played on baser fears).
Now the Vampire has a very old mythos that has been followed more closely in popular culture over the years. When Bram Stoker wrote Dracula, it draws on common elements of the Vampire superstition, but didn't use them as a delivery system for a message he was trying to relay. Now, yes there are themes to vampire stories, like power and sexuality, but they are a part of the vampire mythos and doesn't supersede it (but some stories can and do focus on particular themes of the Vampire).
The problem currently on why the Vampire mythos is so easily forgotten nowdays is because the Vampire is used a place card for various types of stories. In the TV show Buffy TVS, that's a story about relationships (a soap opera if you will) where vampires are used as a vehicle for those stories, but the stories could just as well work any number of "place cards", like aliens, robots, mutants, or even zombies. Same could be said for films like Underworld and Blade. They are both clearly action films, but their "hook" or "twist" is that vampires are involved. Again, you could easily replace vampires with any number of "place cards" and the movies would still work with a little changing.
And that's ultimately what makes Vampires better than Zombies. While Zombie stories can always reflect and comment on the current times, Vampire stories can dip into its own mythos and tell stories solely in the world of Vampires. Zombies stories can't stand on their own because there's no real background to prop them up. They're mirrors or "place cards" to speak to the viewer or reader about issues, but they can be easily replaced by any other sort of creature (like robots, aliens, mutants, trolls, ect). But Zombies stories don't have anything to draw upon to talk about itself. Because to talk about the Zombie past is to speak of other metaphors.
With vampires, there are enough themes and elements built into the mythos that it stands well enough on its own. You can play with the various themes and elements for plenty of stories before you even have to think about looking elsewhere for inspiration (like using the vampire as an action hero or in a romantic comedy). Mind you there's nothing wrong with using vampries with outside elements, but just remember that vampires can be used straight out of the box, no additional preparations necessary.