@PakkonenCT I remember reading or hearing somewhere that it's because of grass. Urban settings don't have grass, but suburban and rural settings do. In wouldn't make sense for people to be mowing their grass during the apocalypse, but it's impossible to find a cheap non urban setting with overgrown grass without building a soundstage, which is too expensive for TV shows and low-budget horror movies.

The only alternative would be filming in a desert.