I think you mistyped here. The point of the move is that $500k in San Francisco vs $500k in any other city in the US (except New York) result in substantially different qualities of life. $500k a year income in Miami can get you a mortgage on a 3 bedroom house and a boat.
In SF, you get a mortgage on a 1 bedroom apartment.
500K in SF gets you a smaller place and plenty of discretionary income. Companies in other places can often give you a house, but not match the discretionary income.
Pay your engineers 500k in a medium cost of living city and you will have the best employee retention of any company once they get used to their quality of life.
LOCATION LOCATION LOCATION!
This. Those salaries are basically correlative to cost living * demand for resources.