COVID hastened a situation that was looming for most cities: non-manufacturing jobs, due to technology, no longer needed to be situated near ports (whether on the Atlantic/Pacific coasts or the Great Lakes). On top of that, they have a massive ageing infrastructure (including their expensive government employee caste), accompanied by huge spending on people no longer sending tax revenues into the city coffers (as the flight of jobs accompanied the flight of property taxpayers and city payroll taxpayers).
The push for “national socialism” (sound familiar?) is driven by the realization that as long as companies and workers can flee to greener pastures in “free states”, then the solid socialist areas are doomed - the geese that laid the golden eggs have fled, leaving just the outstretched palms of the permanent underclass and the government worker caste “administering” them.
Quite right, this process has been happening since the early 1970s or earlier (if you want to count the capture of the industrial base by unions).
The decline of the industrial centers has been happening for a long time. Creeping socialism is a long process. Technology and the buildout of the Interstate system has facilitated the decentralization of industry.
Detroit was the center of the Car Industry and the Car industry was the first to take the hit of the opening of the US markets to international competition thanks to James Earl Carter, the Destroyer.