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I think it has to do with the "Reset" button appeal. Let's face it, the world has become an extremely boring and mundane place. No longer is there any sense of adventure, wonder, or awe; no longer do our lives truly feel meaningful. I think the appeal with zombies is that it would give us some new sort of adventure -- even if it's a crisis -- and thus a break from the mundane. There would actually be something meaningful and interesting going on.
I will also say that I think Zombies and Vampires resonate with people based upon political affiliation. I think that Liberals are more likely to fear Zombies because of mindless consumerism, conformity, and the breakdown of social structures which they place so much confidence in. It forces an individualist spirit. This is why Conservatives love the genre. Similarly, I think that Conservatives are more afraid of Vampires because they symbolize the breakdown of tradition, literal bloodsuckers feeding off of other's livelihood, and a tiny minority forcing us to change our way of life. It forces society to adapt. This is why Liberals love the genre so much.