On top of that some areas outright collapse and are left with a bunch of infrastructure they can't support. The US doesn't really have any good mechanism for dealing with the "single-industry town where the industry collapses". There are a significant number of these in the more rural areas of the country, mining towns and such where the mines dried up and left town. There's no method to
un-deploy infrastructure and in fact in many places there's intentional barriers to "right-sizing". Sometimes you can rip out paved roads and replace them with (cheaper to maintain) gravel roads etc but there's just a lot of miles to maintain regardless, suburban sprawl is a problem but rural/ex-rural sprawl is
massive in the US.
In these areas, what is left is often essentially government welfare. The area runs on social-security checks (which go a long way with cheap cost-of-living, as long as gas prices aren't too high) and government jobs - prisons, military installations, civil positions. And I'm not talking about farm areas etc - that's a local industry too, there are a lot of ex-rural areas where it's almost completely unimproved, the types of places surrounding national forests etc.
What's more, these regions tend to be extremely infrastructure-heavy, there are a lot of miles of road and power-lines per resident, and while sure they don't have sewer, the US's road and power and communications infrastructure are heavily state- and federal-subsidized, state and federal governments chip in a lot on road and power spending. It's effectively a massive transfer of wealth out to regions that are economically unproductive, and while you can argue for or against that as a position, it's pretty unquestionable that money flows out of urban centers and into rural ones, both from government spending and also from service mandates that benefit these uneconomic operating areas (eg in power/telcom).
It's another whole layer on the "growth ponzi scheme" - sometimes the ponzi doesn't just lose its growth, but the market can collapse underneath it too. And it's exceedingly rare that the government entities themselves ever are dissolved as a result - the expectation is that government services are a one-way ratchet.