Sadly, that's because other areas of the US are trying their best to NOT be an innovation capital. There really should be more Silicon Valleys but most other areas in the country don't have the will to do so.
I am not sure it is that simple. The bay area just beats the crap of other places hands down when it comes to starting companies.
Let us look at one of the closest competitors: Austin. This is a city that has a great cultural scene, no state taxes, cheap living, and a good C.S. school close by to get candidates. Yet, there are hardly any software startups in the Austin area. Most folks who graduated with me moved to the bay area. There are more latent variables in what makes the San Francisco bay area tick. If this is the case for Austin's competition, I am not sure how easy it would be for one to inorganically make a city, say in the deep South, become an innovation capital?
The hard parts (colleges, taxes, money, etc) are relatively easy to get compared to the soft parts. I think those soft parts is what makes silicon valley better than most other areas. My theory is that those soft areas are in the cultural part of society, this is the area which the vast majority of people in the world DON'T want to change.
Take one (of many) soft components - acceptance & praise of failure with learning. For some strange reason, this is a hard concept for most people to accept. Many people are shamed by failure or hide their failures pretending they aren't failures at all. They never learn anything useful from their mistakes. They also won't accept people who had any failures. This causes people to have careers of "no failures" which basically means they pretty much only succeed in mediocre things. I don' know if Austin overcame this one example but this type of thinking is a major roadblock in many areas.
Let us look at one of the closest competitors: Austin. This is a city that has a great cultural scene, no state taxes, cheap living, and a good C.S. school close by to get candidates. Yet, there are hardly any software startups in the Austin area. Most folks who graduated with me moved to the bay area. There are more latent variables in what makes the San Francisco bay area tick. If this is the case for Austin's competition, I am not sure how easy it would be for one to inorganically make a city, say in the deep South, become an innovation capital?