Amazon forcing 'voluntary resignation' on employees failing to relocate

I met an Amazon delivery driver yesterday and got to talk with him for a minute. Very nice guy, clearly working very hard at his job, but I couldn't help thinking "why is he working for Amazon?!" Given all that we know, given the conditions in the warehouse, etc. WHY are people still working for Amazon?

I understand in small towns the fulfillment center may be the only job available, but that can't also be true for larger metropolitan areas. At what point will people simply say enough is enough and stop working for Amazon? Never?