I would never try to build an in person team in the bay area unless you need the absolute 1% of engineers on your team.
Some people ended up in the Bay Area, many people appreciated being able to live and work elsewhere. Not least, Europe.
You're not going to get those most places. I'm not sure it's the norm in the Bay Area either though.
In my experience, people mostly look to preserve their financial position rather than take a jump up. Just because rent's cheaper somewhere else doesn't mean I want to take a proportionate pay cut. I've watched people turn jobs down flat when offered 50% of their pay in NYC because rent is half of NYC's.
Salary history matters a lot of negotiating power in the future. Salary matters for building up a financial cushion in case this job elsewhere doesn't work out and now I'm somewhere that has a lot fewer options on offer.
It is absolutely the norm in the Bay Area for salaries even adjusted for cost of living to be far better than elsewhere. Plus all the additional attractive features like a relatively more tolerant population, much more diversity, better public venues like parks, and recreation like museums and such.
I'm also in a position at the moment where I have relatively low overhead (no kids, good health) and realize that might not be the case for everyone, though I'd bet it's the case for many people who don't bother to take advantage of it.
The density of investors and other founders/early employees in Silicon Valley can't be beat, and I often found myself learning inadvertently - dinner table conversations would be about how people raised their round, the friend of a friend you meet while camping turns out to be a partner at a fund you're trying to pitch. In more cases than are logical or fair, people simply invest in their friends - which means if you make friends there you're increasing the chance you'll be able to raise money easily.
That being said, the cost of living is absurd and I would never hire an engineer in Silicon Valley unless I was building something at the outer limits of frontier tech (and even then I'd scour the globe for qualified engineers elsewhere). And I don't think you need to be there forever. If you build up a solid network you can move away and still reap a lot of the benefits from afar / through occasional visits.