Actually, I think the larger talent pool is pretty inescapable. Here's some wild guesses:
There are 3.87M software devs in the USA in a population of 325 million: https://www.census.gov/popclock/ https://en.wikipedia.org/wiki/Software_engineering_demograph...
Call it a density of 1% across the USA.
San Francisco has a population of 870k, round up to 1M.
https://en.wikipedia.org/wiki/San_Francisco
If you assume that SF has a software engineer density 20X what the US does, then they have approx 200,000 engineers available for hire.
Assume that only 25% of software engineers are good for a remote job. That means that you'd have 960k engineers available for hire remotely, almost 5x the pool of SF.
Yes a lot of assumptions above (and there's also a skills matching and discovery issue), but I think that illustrates the size of the talent pool for remote hiring. And that doesn't include software engineers who aren't residents of the USA.