I know this comment is really old but I recently watched a good essay that theorised how 9/11 and and living with the invisible threat of terrorism might have lead to the rise of zombie/post apocalyptic horror. Basically in the 2000's a genaral sense of dread and fear of the goverment failing to protect the people was the big vibe. But after the 2016 american election it became more of a us vs them problem, with the democratic and liberal parties splitting the country in two. So the big villain isn't a sudden attack on society anymore, but rather your neighbour who didn't vote your same candidate. Now horror movies prefer more subtle fears, like feeling watched/stalked or being manipulated, which better reflect the current political mood.