Ultimately, it's inflation. Despite bogus numbers that make it look low (driven by cheap foreign-made consumer goods) the cost of the things people can't avoid paying for (housing, health care) keeps shooting up. People can't continue to work for low wages and keep paying the bills.

Megacorps like Amazon can whine as much as they want that they're "running out" of employees, but the solution is obvious: just raise wages. Once big employers like Amazon start feeling this squeeze enough, they'll start passing the costs on to consumers, and eventually even those Chinese imports will start becoming more expensive. Once that happens, it becomes impossible to pretend that inflation is not real.