I'm from Europe but lived in Pittsburgh and graduated in CMU (software engineering). Really enjoyed the city and the people I've met there. CMU is really a place where you can discuss engineering breakthroughs while having breakfast or a coffee.
It is true that the coffee houses there tend to have their own personality and become really good places to study.
But still left the city and just returned to Europe. I've left because the poverty rate in the city was high at that time (2010) and was too easy to either get mugged on the street or get yourself inadvertently involved in some violent event.
Still, Pittsburgh is a special place in my heart and I still keep contact with friends there. Was happy to read this article, really happy to see the city getting better.
I grew up out west, had family and such out there. That was a big reason.
The weather has been mentioned by others. They have relatively rough winters. Fairly hot and humid summers. Spring and autumn are pretty awesome though, unfortunately that's when CMU was doing the CMU thing and play time was limited.
Perhaps it has changed as Paul suggests, but in the 1990s they were still in their negative pessimistic ways. It was routine to hear locals talk about how the city's best days were in the past. I learned 2 things: 1) when big time jobs leave it takes a long time for the place to heal and Pittsburgh lost a lot of jobs from the unions and steal and all sorts of things. 2) I grew up in a fairly optimistic place, at least a neutral one towards progress and just building things and doing things. They had this negative attitude that just sort of sits on you, I couldn't place it until I really left, but the negative attitude was oppressive. You're young and excited, you want to dream, you want to believe the dream and it's a place where a lot of people have had their dreams go away. A substantial portion of the populace just sort of expected Pittsburgh to fail when it attempted things. I found that attitude rough, it wasn't obvious to me the entire time I was there but it didn't feel good. It's bigger than just Pittsburgh, Wheeling has experienced some rough times, I visited Youngstown once (they had the nearest version of some store where I could exchange some Christmas gift) and it was like visiting a different country.
The tax situation there isn't great. Sort of surprised nobody has mentioned this, there is like a city income tax. And then ultimately, more money is more money, you can talk about the cost of living but iphones, xboxes and cars cost the same everywhere.. I want to say the good starting jobs for fresh grads in the Cleveland/Pittsburgh area were like $50k-$60k in the mid 1990s, out west I made more than that.
PGH is a great town, a lot of character, it's a good town to raise a family in, it has a lot of positives. Surely there is enough money there to spin up some VC funds, I could see it being a small to medium startup hub but I don't know how much it has really changed.
At CMU there's a lot of rhetoric about how bad Pittsburgh is. There's a surprising amount of talk by students at CMU about how much Pittsburgh sucks. Many students never venture far off campus, never actually get a feel for the city itself. Then, once they graduate, the jobs are in SF or Seattle or NYC, so having no other attachments to the area, they move.