I suppose the idea is to work in SV for a couple years while you're still young and healthy, rack up as much cash as you can while living quite frugally, then move to a cheaper place, buy a house for cash (or at least have a solid downpayment), and have no problem finding a job since you have X years of relevant experience at top-tier companies.

The result of fleeing middle class is that you have a city with a strange mix of very wealthy individuals (who can afford the high COL) and very poor people (who cannot afford to move out).