DARPA made Silicon Valley, but Stanford and UC Berkeley — and nearby communities that evolved to become basically playgrounds for the students of them — kept it going. Entrepreneurs came (or stayed) to capture the supply of smart and bored college-aged intellectual labor; and VCs came (or stayed) because of all the entrepreneurs.
But that doesn't mean that seed-stage companies don't move to (or stay in) the Bay Area these days primarily because of the VCs, rather than because of the talent. Talent is free to move anywhere it likes — especially these days. An entrepreneur will find just as many potential employees for their startup in literally any college city.
But tech VCs (and especially ex-tech-entrepreneur angel investors) will, despite having a presence in many places, mostly still live and spend their free time in the Bay Area. And so you'll be much more likely to have your name on their lips if you're showing up at local events they attend, bumping into them at restaurants, meeting them on the golf course, etc.
Let me put it this way: every Canadian seed-stage startup I know of, has their CEO regularly fly to the Bay — even if they're located on the east coast of Canada! — to rub shoulders with the Sand Hill VCs, in hopes that they'll get more attention there.
You're putting the cart before the horse. Investors live all over the place, and large funds have offices in markets where there is a signifcant number of possible high growth companies to invest in. And they'll invest where they don't have an office and always have.
The reason why so many investors are in silicon valley and san francisco is because of the companies. And the companies are here because of the environment. I've worked around the world but the reason I love working in the valley (specifically the peninsula) and not elsewhere, not even SF, is because of the extreme density of people, resources, markets, and just the sheer intensity of the place. I hire from all over the world, but really, just getting shit done is so much easier around here.
Ignore the bros. Those assholes get the press 'coz they're interesting to write about. I'm talking about nerds in true tech businesses like hardware, software, mechanical systems, pharma.
It's not for everyone, and even people who would like it may choose elsewhere for other reasons. Those decisions are all legit too.