The bottom line is that smart people want to be around and work with other smart people who are like minded. That is why you see so much talent attract to certain cities whether its NY, Chicago, LA, or the bay area. Here on the west coast the vibe is much more relaxed and laid back which a lot of people in tech and other industries prefer. Add in the fact that its sunny most days of the year and you don't have to deal with snow, humidity, or a lot of rain and you can attract talent from a lot of local top level research universities and there is your answer. Smart people who hate the idea of wearing a suit to work and prefer a laid back climate move to CA, just the same as smart people who want to be a big playa in finance move to the NY area.