This is not an uncommon phenomenon. There are still some habitable enclaves within the city limits.
What often happens is that young married couples frequently bail on Chicago when their offspring are ready to enroll in school. With the exception of a handful of privilege academies (reserved for the wealthy and the politically connected), the Chicago Public Schools are a pathetic joke despite insanely high taxes wasted on public education. Parents are faced with two alternatives: finding an affordable private school where they can pay tuition (which is becoming more difficult as the number church affiliated schools are dwindling) or relocating to suburban school districts where children can be enrolled in better quality public schools.
Once the children graduate and move out, it is not unusual to see empty nest parents downsize and move back to the city, provided that they can find an acceptable house or condo.
That used to be a trend, now it's far more common to see empty nesters and retirees leave the state because of the high taxes and fees. Especially since Kim Jun Pritzker came to power.
Gogeo's Law #4...quality of public services varies in inverse proportion to funding.