Part of it is likely density of companies, talent, funding, advisors, etc. The whole ecosystem for starting a technology focused compnay is right in your backya

Part of it is likely density of companies, talent, funding, advisors, etc. The whole ecosystem for starting a technology focused compnay is right in your backyard. In my case, I live in SOMA, and was recently looking for a new job. I talked to 20+ companies, all of them within a 30 minute walk of where I live. I can easily head over to a friends company for lunch and learn about what they are working on. Or invite a former co-worker to our office for lunch to try to recruit them. All of this is maybe 15 minutes travel time in SF. I don't know how to quantify the value of this, but I don't see it being replicated anywhere else. And then combine that with a very open culture, where people are happy to share details about what they are working on, it really helps to accelerate learning. I lived in Seattle from 1999 to 2009, and did not experience the same open culture there. Maybe it's improved since, but I was amazed at how much people would share when I moved to SF.