People moved away when heavy industry collapsed in the USA 40 years ago, because people in Pittsburgh tend to be hard workers who are loathe to sit on their ass waiting for a check like in some of the other cities on your list. They left to go where the work was, which is why there is a Steeler Bar in every city.

People came from all over the World to work making steel in Pittsburgh in the 19th Century, and now they are coming from all over the World to work in medicine, robotics, and scientific research. For your information Markie, the immigrants moving to Pittsburgh now aren't poorly educated non-English speaking farmers who snuck across the Rio Grande. They are scientists and doctors who have advanced degrees, many of them earned at Pittsburgh universities like CMU and Pitt. If people don't want immigrants like that, it can only be racism.