[jimmaswell]

Because a certain amount of local density is needed to support any establishment's existence. The more specialized it is, the more local population is needed to sustain it. As the middle class shrinks or other economic changes happen, the margin of this can get narrower, as shops consolidate into having less locations in denser areas. There apparently used to be a lot of full time IBM positions near where I grew up, but now those buildings are mostly abandoned.