People like zombies. People are fascinated by zombies. My town has a freakin' Zombie Walk every year.
Monsters are a big part of the social zeitgeist: what society as a whole feels that it's needing, or missing, or afraid of, will become an icon in that society's media.
Apparently, modern corporate-capitalist-consumer society is fully cognizant that it spreads like an infection, leaves ruin and devastation in its wake, and has absolutely no braaaaaaaains at all.
Also, for some reason lots of people like making "would you survive the attack of the zombies" tests on OKCupid. This test will determine -- in a manner just as scientific as those tests -- whether or not you would have the skills to write a test JUST EXACTLY LIKE THOSE.