As someone who went to CMU, there are just so few investors in Pittsburgh. In fact, many years ago I was talking with Severin Hacker (Duolingo cofounder) about some of the challenges of running a company there. There is a lot of engineering talent...and that's it. Marketing? Business development? There just aren't (or weren't) that many people there. I also know that Anki moved to San Francisco because it was the only way they could raise money. I also left Pittsburgh because it was the only way I could raise money.

So long as the investors are in the Bay Area, it will continue to be the startup mecca of the world. That does seem to be slowly changing, but not nearly as fast as anyone promoting their city as the next startup hub is willing to admit.