I might be wrong (because I often am) but I suspect that our interest in zombies might wane as the world 'gets back to normal'. We've been living in a time of upheaval and anxiety not seen since the 1960s-70s. It's a crazy time. People are scared. They need a place to channel their apocalyptic anxieties. Zombie stories are perfect because they are real enough to scare us, but not real enough to keep us from sleeping at night. I think when the world calms down, as it did in the late 1980s-1990s, people might want to move on from thinking about the end of the world.