Quite a few of these were produced out of Google and FB, so it makes sense they would be based out of MV/Meno Park.
However most of the unicorns or near unicorns since 2010 have been based in SF. Dropbox, AirBnb, Uber, Lyft, Stripe, Zenefits, SoFi, Credit Karma, CloudFlare, DocuSign, Wish, Slack, Github, Instacart, Prosper, Automattic, Eventbrite, Okta, Docker, Gusto, Nextdoor.
Let list could go on and on. I stand by my statement that more talent in concentrated in a smaller area vs South Bay and they are trying out a lot more things and also faster. Dynamics of an urban area also play some role where, where you can quickly walk to, use public transport or get an Uber, vs driving to another place in South Bay. All this leads to SF being ahead of South Bay in terms of learnings and trying out things.
And name calling doesn't get us anywhere!