Also, in order to be paid that much, you usually need to live there. It all depends on how you value certain things.
Ample parking, day or night: $2500/yr
People smiling; kindly neighbors: $5000/yr
Public schools that don't suck: $15000/yr
Parks/public spaces that you actually want to visit: $2500/yr
Low violent and property crime rates: $5000/yr
Political and cultural compatibility: $2500/yr
Good local television and radio stations: $1250/yr
Things like that add up, and are highly subjective. But when I see significantly higher salaries in very specific geographical regions, what I see is one of two things: either people there tend to be more valuable than others, or they are demanding compensation for all the crap they have to put up with and/or purchase that they can get for free or at reduced cost elsewhere.
For instance, in Chicago, I had to pay an extra $100 a month for a parking space behind my apartment. That's $1200 a year already. Never mind if you actually wanted to go anywhere in your car and park in the same ZIP code. That costs you additional time and walking distance or additional cash. And it certainly impacts your property and casualty insurance premiums.
Having grown up in a different city, where parking had never been an issue, that threw my own freedom of movement up in stark contrast, as something that had calculatable value to me, and which likely differed significantly from other people. The costs of having a car in Chicago were only partially mitigated by having CTA and Metra commuter service. Grocery shopping is a lot different when you can only buy what you are willing to carry in your arms for as long as it takes to get home. You buy a lot less of the things that are mostly air (additional volume) or mostly water (additional weight).
That was but one of the reasons that I found the local pay was not worth the local costs, and moved.
For a variety of reasons, the people deciding on the location of a business do not value those local costs in the same way, and do not realize that their employees may demand more in compensation because of them. Or they just don't care.
As for myself, I could probably get 1.5x my current pay in SV or 2x in NYC. But it would have to be 3-5x to be worth it. I currently rent a 3br 2.5ba house for about 12% of my gross pay, and can drive to work in 20 minutes. Is that even possible in SV or NYC on income less than $15 million a year?