This seems like a somewhat unexpected result from the growth of the internet.

At first glance, it seems like the internet should allow for a more geographically distributed economy, and make it easier to get a job regardless of where you live. Instead, the internet has concentrated jobs in cities by making it easier for a few companies to sell services to 'everyone'.

Instead of going to a local store or even a local Walmart, people purchase from Amazon. Instead of doing taxes with a local accountant, more people use TurboTax. Instead of a local lawyer, there are services like legalzoom.

This centralization is likely a big part of what is causing this. This effect will probably continue unless the large internet companies move to a more geographically distributed workforce.