And programmers tend to move where there are tech companies.

Less so. If you want to play in MLB (and you do, because that's where any of the money is) then you have to move to where there's an MLB stadium - the team isn't going to move to you.

Whereas, there are many more software companies that pay roughly the same wages all of the world, and companies offer remote work, which will reduce the differentiation - but not eliminate it.

That's why I said "tend to move", yes.

> there are many more software companies that pay roughly the same wages all of the world

The jobs with the really high salaries (and arguably the most exciting coding jobs) are disproportionately located in a handful of major tech hubs.

>there are many more software companies that pay roughly the same wages all of the world

I question whether there are many companies that, aside from executives or other high value employees, pay similar salaries around the world. I imagine at least some pay comparable salaries across the US--or at least salaries that don't completely follow CoL--but pay Indian or Chinese developers what they pay Bay Area ones? That seems unlikely at any scale.