While re-reading and revising the question, maybe I found the answer myself: the author doesn't mean all companies in the region when they say "all companies" (

While re-reading and revising the question, maybe I found the answer myself: the author doesn't mean all companies in the region when they say "all companies" (emphasis theirs), they mean that for job X (like developer), a supermarket is not trying to hire developers from other countries or continents. It's about the size of the pool of people that can do this job, not whom a company competes against with their product or service. Supposedly Disney doesn't hire globally just like the local supermarket whereas GitLab does. Why one would and the other wouldn't for the same type of job sounds like just a measure of wealth (a local supermarket wouldn't be able to pay for someone's relocation and competitive salary with other places in the world they could have gone to, and according to the author, Disney doesn't either), making this whole classification seem to get causality backwards. It's not that you earn more there because they're hiring in a broader pool in their greater desperation to attract more talent, it's that one simply pays more because they have more money in the bank to pay out, and that allows them to hire from a broader pool. In a good case, that then also attracts the better talent to keep up that greater money inflow.