Think of it from the perspective of the countries great engineers emigrate from. They lose the potential for their own economic growth and prosperity, and send their best to be shackled to a company in the US where they need to keep a job or be deported. It is possible, but very hard, to be entrepreneurial in that environment.

But that is an essay and a half of nonsense to get into, about why they need to immigrate in the first place in such large numbers. In the same way monopolies are not healthy in any industry, having all the "great programmers" in the bay area would, I feel, stunt the potential of the industry by creating an insular monoculture.