The Conservative Planner pins the problem (naturally) on "progressive planning efforts aimed at strengthening formerly dilapidated urban neighborhoods.":
"What is keeping families from coming back to these cities?
Affordability is probably the biggest contributor to this, given that most re-claimed neighborhoods have been gentrified to a degree which few middle class families can entertain the thought of buying a residence despite advantages in terms of walkability and access. Forget having a yard or a place for the dog to drop."
A jobs/housing imbalance is also to blame, says The Conservative Planner.
Thanks to David Sanderson