[dragonwriter]

> That clearly didn't actually happen when the jobs first migrated to the suburbs.

Yes, they did; not so much in terms of density, but the suburbs that had substsntial local quality jobs rather than being bedroom communities for more distant urban areas (or other other suburbs) did become substantially more expensive (as is expected, because convenient location to work is something people value), and, conversely, when jobs have moved away (including in the return to cities) they've gotten less expensive.

There's also the fact that major cities tend to be located in places which are geographically conducive to physically supporting largee numbers of people and large volumes of material trade, and even if an industry doesn't itself need or produce lots of physical goods directly, it often supports or is supported by others that do, and, in any case, the ability to support people effects the economics of moving jobs.