It's Not About The Monsters, Stupid
Ultimately, all of these traits that have shuffled vampires away from leading monsterdom have something in common: They force us to engage with the vampire individually. Give a vampire a history, give him a sense of self-preservation, give a vampire a plan and a name and something he wants, and you've created something complicated. You've created a monster you have to interact with partially on his terms, because he's got a say in how things are going to turn out. You've got a situation where the conflict is partially about the monster.
Zombie scenarios, on the other hand, aren't. They're about the survivors, and the vast majority function as pats on the back to the protagonists for being stronger, smarter, and cleverer than the poor schmucks who got caught by the zombies. The monsters are in a sense incidental, there to make the humans look good and to allow the reader to identify with those stronger, smarter, better-prepared protagonists.
And zombies will let you do that to them, because that's what they're there for: to surge mindlessly and hungrily, to stand as examples of what the human protagonists are not, and to be scary by dint of simple, easily-understood directives. That's not to say they're not monstrous, but they're a sort of monstrous that's easily controlled, directed, and diverted to the author's ends, and that doesn't necessarily raise a lot of questions beyond "How many rounds you got left?"
Vampires don't let you get away with that, not even the sparkly ones who sit mooning over what is, after all, lunch in a very pretty package; they all still have motivations and individual approaches. And by doing so, by seizing the narrative initiative in even the smallest ways, they take the spotlight away from the human protagonists - and by extension, away from us, the readers and viewers.
So bring on the zombies. As monsters go, they're much less demanding.
Richard Dansky wrote Clan Novel: Lasombra as part of his radical anti-zombie agenda. Clearly, it failed.