People who work in grocery stores/gas stations in affluent areas typically commute from less affluent areas.
I've heard from actual coworkers who live in San Francisco, that even high paying engineering jobs have trouble making rent without roommates or dual incomes. Do they choose to live there? Yes. Can they move further away? Also yes. Do they want to commute 2 hours each way every day? Probably not. Add in taking your kids to school, and suddenly, the choice you think they had is really no choice at all.
Technically, we all have the option to quit our jobs, find a track of land in the middle of nowhere, and live off-grid, but do we? No. Choices aren't as simple as "find somewhere else to live".