I think the phrase “working as a Walmart greeter” is just a euphemism for a job that a senior citizen is forced to take in their later years in order to survive. I don’t think it’s meant to disrespect the work as much as try to convey the sad situation that a senior citizen has found themselves in. Of course, if the senior citizen just does it because they want to be busy, that’s a different matter. I don’t go to Walmart often, but I don’t recall them actually having greeters. It’s not a reflection on honest work which I hope we all honor, it’s a way to convey a situation the person has found themselves in.
If I say I don’t want to end up “living in a van down by the river”, is that disrespectful to RV’ers or homeless people? It communicates a situation.