Zombie movies are great, especially when done in a fresh way, like Train to Busan. I like that the genre was started as a critique of consumer capitalism – mindless people consuming everything in sight, set in a mall.
Zombies are consuming a finite resource (humans) and they do it so that the resource cannot multiply itself, zombies represent unsustainable capitalism.
Looking at it in a dialectical way, zombies are often caused by research and experimentation. Unlike other disaster movies where the threat is always without, zombie movies show us that human activity itself carries the seeds of the destruction of our civilisation. In disaster movies there is a threat that the whole Earth will be wiped out, the damage is always total. In zombie movies, there is no such expectation. Zombies are ultimately a threat that can be defeated, either by killing, or by hiding in a bunker until they die off. In zombie movies they're always fiddling on the radio, trying to find army bases (yeah, shit implication), and so on, implying that no one assumes that zombies can get everyone on the planet; unlike an asteroid that destroys all life on Earth, or the Sun dying, or the Earth's core stopping rotating, etc. Zombies are a threat to our civilisation, not on human life. Human life will continue, even if it is some fucked up mad max society.