In spite of what the article claims, the vast majority of employers do NOT let you work remotely 100% of the time. They are mostly located in the big/expensive cities, so that's where developers will go. There's really no mystery there.
Best place to start a business is where you have easy access to a large employee pool for your specialty. Best place to locate yourself as a specialized employee is where your industry concentrates a large number of employers.
This is true if you're in software, finance, film, ....