We don't need these bases for sentimental reasons. We don't need them because local congressmen want the jobs and money they provide. We don't need them because we must never change the structure and operations of our defense system. We need them because someday they may very well help us survive as a nation. Seems worth the price, doesn't it?
This of course is pure guessing on my part. I can't prove it with data. My gut says that when things turn dark, we will need all the help we can get.
Another reason to have bases well distributed is that it anchors the military in a symbiotic way to the country. A major military base serves as an economic and political anchor for a given area; it's much easier for people to understand what the military does in peacetime and wartime if, well, the military is part of their everyday lives. In that way the intangible benefits of many bases in many states is better for the body politic than to have fewer perhaps more efficient 'super' bases.