I believe your suspicion is unfounded, so there! (two can play that game)

Who defines, "living wage?" That's another useful phrase that means whatever anybody says it means.

Nobody forces people to work at Walmart. Nobody forces people to stay at Walmart. Working faithfully for Walmart a few years will provide the worker with a track record that, if she chooses, will fatten her resume' for a higher paying job elsewhere. Costco, perhaps.

Why would any employer, anywhere, pay somebody more, for the same job they have been doing for several years? Whether picking grapes, flipping burgers or stacking shelves, one soon reaches a plateau of competency that is worth a certain amount and no more.