Economic theory suggests that regional inequalities should diminish as poorer (and cheaper) places attract investment and grow faster than richer ones.

If someone is going to invest in a cheaper area, why should he do so in Middle America as opposed to in an even cheaper country? Why get cheap labor in Mississippi when you can get cheaper labor (and fewer environmental and labor regulations) in Chihuahua or in Hubei Province?

In the past, if investment flowed to the lower cost of living places, which led to relative economic convergence for the U.S. states as it mentions, why should investors do so now? It almost seems like a reason for Trump's NAFTA stance. Additionally, when prices go up, we'll get that inflation the Fed's been looking for (only partially /s)

What to do? One answer is to help people move. Thriving places could do more to build the housing and infrastructure to accommodate newcomers. 

Where and why? I live in Ohio, and do pretty well on my salary. Meanwhile, if I took my savings to California, or an East Coast city, I'd be poor by most measures. Am I going to get a job there, with no local connections, and possibly without the skill set that the businesses in these locations are looking for?

Plus, suppose I- a young adult- do leave. What does that mean for the older individuals in my town who cannot? The areas will still decline, perhaps at an even faster rate. Will people move reciprocally from the coasts once they've made their money? Perhaps to the state, but not to the "run-down" areas.

I don't think the disparities are as bad as the numbers suggest, due to differences in cost of living. While incomes might be different in San Francisco, CA and Akron, OH, the same amount of money will get you much more in the latter, meaning having only 75% of a Californian income is not as far off as it sounds.