These people have some warped priorities, no question. I fully understand the desire to live and work in a city with as many offerings and opportunities as New York City. Hell, I moved there myself. But if you get to a point where your financial situation is so dire that you can't even afford to take advantage of any of those opportunities, what's the point of staying and torturing yourself, when you could move somewhere else and live like a king on the same salary?
That said, this is not at all a problem unique to New York, or even big cities. I now live in a dumpy burg that is rated as the second least-expensive city in the whole of the United States. But it's well known that almost all the thirtysomething and fortysomething "rich people" in town (pretty much all physicians; not many young people with a lot of money would otherwise want to live here) are just barely getting by. Why? Because they're all obsessed with "keeping up with the Joneses." They buy hideously overpriced plots of land in "exclusive" snob estates on the outskirts of town and build huge houses to live in, just for bragging rights. Most of their big salaries go to pay for their mortgages and heating and cooling the house, and as a result most of them barely have enough money left over to buy groceries.