The problem is that outside of a few tech hubs, most companies are unwilling to pay developers salaries that even come close to what they can make in a tech hub. So the best developers move to the tech hubs, where the jobs tend to be more interesting and pay better. Plenty of people would take a 25% pay cut to live in a cheaper city than SF, but the reality is that they might have to take a pay cut of 50% or more, and even when you adjust for cost of living, that sort of pay difference is still dramatic (housing might be cheaper in many cities, but car ownership, healthcare, groceries and your kids' college tuition are largely the same).
You don't even need to move to the middle of nowhere. Basically anywhere else would work. Even San Diego is rather substantially cheaper than the SF bay and the weather there is orders of magnitude better.
Sure, I'm not saying pay people the local prevailing wage. I'm saying pay people the same and let them keep way more of that money, or hire more devs, or have nicer offices, or whatever. Just stop handing it to landlords in the Bay.
Sure enough, other cities are up and coming, but it takes time.