“How come there’s only one high-tech cluster.” After all, if industrial age capitalism had just created the prosperity of the Detroit area in its heyday, we’d look on it as a huge bust. But we had lots of industrial production clusters, of which the Detroit automobile industry was just the most famous.
I think there are two reasons why high-tech jobs are clustered in Silicon Valley as opposed to scattered, as were industrial jobs, primarily across the Rust Belt.
The first is size. Industrial plants took up a lot of room. So too did their suppliers. It made sense to have several of these centers clustered around various cities.
The second has to do with innovation. I think that all of the new tech companies have something to gain by their proximity to one another. Discussions happen and new ideas are born. It’s the lifeblood of the industry (after investor money, naturally).