People didn't abandon the cities - the cities abandoned the people. They became liberal, grabbing more and more of what people earned. So the earners escaped, just as one would escape a communist country.
I'm guessing that you're probably young so you don't remember events like the Hough Riots in Cleveland. Or the Black Panthers knocking on doors on the east side of Cleveland, telling "whitey" to get out of their neighborhood.
Watching one's neighborhood turn from a cozy, friendly place where everybody took care of their property to one where homeowners took no pride in ownership. Where they let their own homes falter, dragging the value of the neighborhood down with it. Tenants destroying the property that they rented, and then blaming the landlord. And the cities - they could have cared less as long as they got their tax dollars. In fact, they often took the side of the tenents.
I worked those neighborhoods as an electric Meter Reader for 3+ years. I've seen it up close and personal.
After you've seen a city or a neighborhood get destroyed by liberalism, you won't want any part of it any more. My family fled Cleveland in 1959, and many of my friends' families did so during the '60's and early '70's when things had gotten really rough (thanks, LBJ, for that "great society" mindset). I would never go back to that hellhole, and I wouldn't expect that very many others will either, unless they live in some gated community or one of the few remaining enclaves of sanity.
First of all, let me clear something up I’ve had to clear up several times now. I’m not criticizing the suburbs. I’m criticizing people who feel a sense of entitlement about living in the suburbs.
Liberalism failed the cities. However, the suburbs may no longer be a viable alternative for a lot of people. People may start to move abandoned cities and try to fix them, and not with any big government programs. Alternately, they can build new cities or expand existing ones. With the internet and the availability of air travel, you can put a city just about anywhere.