It's worse than us simply becoming poorer. It's that these places - sprawling low density suburbs - where never financially sustainable to begin with. They never brought in enough tax revenue to remotely cover the expense of maintaining all their infrastructure. There's just too few people per square mile to pay for it all at the property tax rates people can afford. We've only kept things going this long through a few mechanisms:

Letting older suburban infrastructure decay to well past its replacement state.
Relying on growth to prop things up. (Build new neighborhoods and require developers to repave streets and replace/upgrade utility infrastructure in an area.)
Relying on ever higher levels of debt.

It isn't financially sustainable. It was never financially sustainable. As long as a town can keep growing, they can keep the Ponzi scheme going for a time. But eventually you hit a wall on that and the whole house of cards collapses.