Zombies aren’t scary. They’re popular movie monsters because, while looking vaguely human, they’re sufficiently “othered” that you can kill them without remorse (thus acting as a convenient stand-in for other groups that the audience wishes they could do that to) and because they represent an apocalypse that kills most of the people but leaves the stuff behind, meaning that you don’t have to deal with society anymore but you’ll still easily have a roof over your head and food on your table (albeit mostly canned food.)