It would depend on what story they are in.
In most modern stories ... They are merely a plot device, and aren't a metaphor for anything.
What are zombies metaphors for?? I'm unsure they are all JUST about consumerism within society.
Actually, this is a worth a look:
https://www.activistpost.com/2012/05/5-reasons-zombie-apocalypse-is.html
The working class. It is an unflattering metaphor, but it isn’t difficult to see the comparison.