I know and zombies were a niche thing a couple decades ago.
Why is WALKING DEAD the highest rated show on TV?
It’s a reflection of the culture.
Because it's a classic "western" without all the worn out historical cliches. Americans LOVE that tableau.
There’s always some horror beast that’s popular. Before this big zombie wave vampires were huge for 15 or 20 years. Before vamps it was slashers. Before slasher radioactive monsters. It’s not really a reflection of much other than the copy cat nature of entertainment. Once something hits big others will try to follow the formula.