The children of those families are staying in those suburbs. The suburbs need help, particularly with their architecture of the 1950's and 60's. It's mundane and routine. But after two or three generations, those standards will change, the architecture will change, landscaping will change, trees will mature. The neighborhoods will have a very different feel to them.
Sprawl reflects social progress more than decline.
Suburbanization has been going on for centuries. People have been building cities for thousands of years, and this development has spilled out into the hinterlands. Most inner-city neighborhoods were once suburbs of a downtown core. It's just that these outer neighborhoods were annexed into the big cities before modern post- World War II suburbs decided to create their own, independent identities. More importantly, suburbanization represents a significant improvement in the quality of life for people who settle there.