not the parent, but I can think of the major research labs originally in SV, now major tech companies, and the big universities such as Stanford with great technical talent. Those are big factors in what makes SV technically strong.

There's also many country-related advantages not specific to SV but to the U.S. in general: How easy it is to create your company and work from your garage compared to other countries. This makes SV business friendly

The international crowd in SV: People from every continent share and mix their ideas, this usually leads to great results since the people who immigrate to SV for the purpose of entrepreneurship usually all share that great ambition and can bring the best of their home countries cultures and know-how.