Well, as a former resident of Silicon Valley... which includes cities like San Jose, Campbell, Cupertino and many others... I think it began as function of California just being a great place to live! The weather is mild, you're close to lots of cool places to see like San Francisco, Carmel, Los Angeles, etc. And then, because it is a place in demand only those with some dough can afford to live there. That creates a vacuum of sorts, inviting more like minded/wealthy individuals to the area.
Now, in 2000 the dot com industry tanked and a LOT of people had to bail out of SV because they could not afford to live there anymore. I've heard though, that (property) prices are going up again and while it's no where near where it was in 1999, it may be in just a few more years!
Does that sort of answer the question??
Lyte