[selectionbias]

I think this misses a possibly very important effect: agglomeration. Programmers in the Bay Area were not all born there, many (most?) chose to move there, some from elsewhere in the US, some from abroad. If those programmers who are more skilled tend to move to this area then the resulting greater productivity could explain higher pay. So why might more skilled programmers move to the Bay Area? Perhaps because other skilled programmers live there, and programming skills are complementary. A highly skilled developer may be worth more to a company with other skilled developers who can work together to create advanced products. Note that local PISA scores are irrelevant if people were not educated in the place that they work.

[angarg12]

People underestimate the power of human connections and (tech) hubs. The job market is still far from a cold, optimal algorithm.

I was born in a cheap city in southern Europe, and all my life I moved to increasingly bigger and more expensive cities. Why? In my home town job opportunities are very poor. Local jobs are scarce and for full remote positions you are competing globally.

Sure, London is expensive as hell, but there are many more opportunities, so I can progress my career, and drive up my salary. A bigger talent pool attracts more companies, more job opportunities attract more people, and so the snowball goes...

[outworlder]

The siren song of Silicon Valley reaches far and wide, and is difficult to ignore.

[robocat]

They cover that under heading “ 3. Most "good" programmers move to the high-income countries”