A massive chunk (if not majority?) of those top 20 metro areas are largely car dependent for most of their populations. Large areas don't have any public transit at all, and the rest is often designed to be actively hostile to pedestrians.
Try living without a car in these places, all in the 4th largest MSA.
And even in most of those metros (OK. Leave aside Manhattan), not having a car tends to imply a lot of lifestyle choices in terms of activities, visiting friends outside of the metro, etc.
There are certainly people who are OK with living like they did in their urban school for a few years after graduation. But that's not a long-term solution for most people.
