I have a running theory about where the Pittsburgh accent came from.
I think it comes from the mill days. The mills were loud, and people had to shout over the din of labor. When you speak loudly, you can’t maintain all the tones and inflection that words normally require for ‘articulate speech’.
Try it: see if you can ‘talk like a Pittsburgher’ while shouting. I’ll bet you a Yard of Iron (at Chauncey’s, but they’re gone) that you can.
I bet you can get your point across faster that way, then taking the time to try to properly-form words while speaking loudly … like you’re shouting over the noise of a mill.
So I think that Pittsburghese is a kind of “mill-speak.” A utilitarian accent that took hold in our home lives and culture.
I presume that, were we to have audio recordings from the region, before and throughout the coal and steel boom times, we would see the accent slowly develop. We could probably also look at other steel/coal cities around the world, such as Bilbao, Spain, and see the same trend.