I don't think this is actually true - either that it happened quickly, or that how quickly it happened was a surprise. Detroit (the city, which was always the "problem") depopulated from the 1950s onwards as the major industry moved to the suburbs, and the effects were obvious even in the 1960s. It took another 40-50 years to hit the bottom though.
That said, the population is now growing again (since 2021).
It's better than $0, which is what most places pay you to move there.
There are some areas up in the UP that are bad, but very few people live there and they know what they’re signing up for.
Meanwhile, the people I know who live in NJ got wrecked by snow repeatedly this year, multiple feet at a time. I don’t recall ever getting anything like that around Detroit.
Of course, I was in apartments with covered parking and snow removal services the whole time, so I didn’t need to care too much.
I do remember the guys in the Chicago office talking about when they got a foot or so of snow and had to walk to the nearby hotel to spend the night, because it wasn’t safe to drive home. I heard stories like that from people in the Michigan office too, but in my 20 years working I still never ran into it. Just lucky I guess.