It's no longer cheap to live there. Tinkering with new ideas on some modest amount of savings and "odd jobs" or consulting is no longer possible. Expensive real estate leads to calcification and risk-aversion and cultural death. It's why urban ecosystems (including VC-istan, which is not a city per se) turn into hellholes shortly after their peak of greatness.
Enter VC, which connects people with the resources (funding) to try out their ideas and, better yet, enough resources that they have a "rocket fuel" advantage over any competitors. Over time, the VCs and "tech press" became king-makers. Then, the well-connected became a new, informal, executive suite who care more about protecting each other than genuine competition.
Hence, VC-istan. It's the first postmodern corporation, cleverly designed to look like a free market. Reputable investors are the executive suite. People with the authority to write welfare-checks-I-mean-acqhires at big companies are The Compensation Board because they decide on bonuses. "Tech press" are another part of the HR department that writes performance reviews. So-called startup "CEOs" are semi-independent PMs. Software engineers are peons who work long hours because they haven't figured out yet that they work at a big company and aren't actually going to getting investor contact and made founders in 7.35 months-- that was a degenerate empty promise.
VC-istan has clever marketing. It doesn't look like a stodgy corporate behemoth, but it is. That is why it has ceased to innovate.