I took one of my kids to Pittsburgh for a college visit a few years ago, I went expecting a run down former steel town like Detroit and left fairly impressed.
The short answer is Pittsburgh has become a hotbed of tech start-ups, largely driven by the top ranking computer science and engineering departments at Carnegie Mellon University. CMU's AI research is arguably ahead of school's like MIT and Stanford so everyone wants a piece of the action, companies like Apple, Google, Facebook and Uber are pouring money into Pittsburgh and a significant amount of venture capital has started coming in as well. This economic injection has led to growth in all kinds of other industries like craft breweries, restaurants and bike shops. I literally saw a bike shop with a craft brewery in it, or a craft brewery with a bike shop in it in Pittsburgh, if ever there was a sign a city is being overrun with hipsters that has to be it. Apparently mountain biking and rock climbing are popular activities in the area making it an appealing city for those outdoorsy nerdy types that find Northern California or Colorado too expensive.
Spending some time in Pittsburgh it felt to me like it was on it's way to becoming another Denver or Seattle which are certainly places many young people want to live. Unlike other tech hotbeds, Pittsburgh is still an affordable place to live, I could see it being a great place to settle down and start a family. Weather wise, it's certainly no California, but the winters are more mild than the Northeast like New York or Boston.
There are tons of articles talking about the sudden growth in Pittsburgh:
https://news.crunchbase.com/news/pittsburgh-an-emerging-hotbed-of-robotics-ai-companies/
https://www.inc.com/magazine/201805/jill-krasny/destination-pittsburgh-pennsylvania.html