Destroying their financial future? None of my friends living in SF or NYC make less than $160k a year working as engineers. In fact, they make that nearly right out of college. The more senior engineers (5+ yrs exp) bring in $300k-500k a year.

They save a significant amount of it, more than they would have saved in any other place. And they can leave at anytime to a low-COL place and buy a house in cash.