The startup sector is centered here because the money (VC firms) is here. The reason for that is largely historical accident.
And, weather doesn’t adequately explain the high CoL anywhere outside California or Hawaii. “It’s where the jobs are, so everyone wants to be there does,” and it also explains California. (Hawaii is special— it’s an archipelago, so, cost of shipping goods plus weather is really the best explanation, given the lack of a compelling employment story.)