Why SF? Why not India? UK? Or anywhere else?

Concentration of education (Stanford, Berkeley) and money.

Edit: And some historical momentum

Why India? Other than being an outsourcing center, India's tech product offerings to the world are almost non-existent; (maybe zoho); without a product and entrepreneurship culture, India makes no financial/strategic sense for startups/bigwigs.

If not SF, another American city would have been the tech hub. The enterprise and consumer markets were in the US. The tech companies served those customers. Or at least they used to. Now with corporate financialization and the rogue administration and supreme court, the US is rapidly destroying itself.

I have a long-standing theory that the most significant factor is the weather.