How do you know it's abortion? There's no evidence that there's a greater percentage of single-issue abortion voters now than before, especially in southwest PA. The umbrella area that abortion falls under is moral values, true, however, the percentage of people who voted on that issue has actually fallen in recent years.
SW PA is heavily Catholic. For whatever reason, it's a bigger factor in Presidential voting in SW PA than it's been for a while.
Recent Democratic presidential campaigns have ignored economic issues too much... and they've lost.