An explanation is the overbuilding of commercial property space during the late 1980s plus land speculation and redlining -- in short uneven urban capitalist development -- with a good dash of racism and crime-hysteria by the white professional elite who, aided by new communications technologies, have vacated to favoured walled-up edge-cities.
> From: "Max B. Sawicky" <maxsaw at cpcug.org>
...
> Even better, there is vacant or underutilized
> land in cities themselves, contrary to a
> remark I dimly remember in the thread. To
> some extent, this is already happening as
> the costs of suburbanization mount and begin
> to become noticeable to suburbanites, such
> as the cost of new infrastructure, time
> required for commuting, etc.