Or they are not willing to accept the loss of income stability from living in a place with lower commute times, which also end up having fewer opportunities to earn income. Plus once a spouse also needs to work, both people's income streams and future stability of the income streams have to be managed.

Due to increased volatility and concentration of places with sufficient income earning (and increasing) possibilities, this manifests itself as cities with lengthy commutes for all except the luckiest.

Edit: Also compounding this is that school quality is roughly a measurement of the income earning abilities or wealth of the children's parents. It's known to everyone that sending your child to a school with children who have lower income parents results in lower chances of success for your child. If you want to mitigate this, then your options are to send the child to a private school, which are very expensive in cities, or move sufficiently far away so that you are geographically too far from the children with lower income parents and so the public schools' children end up having parents that have similar earning potentials.