The PGA tends to be played on more traditional PGA tour courses - "target golf" locales. Euros do better at Augusta and the US Open rota courses, as a rule.
Rai is a pretty good player - 3 worldwide wins - but Aronimink didn't cover itself in glory. Ross is obviously one of the greatest course designers in history but without really punitive rough the PGA tried to gimmick the course up to avoid it being blitzed. When you see a bunched up leaderboard with so many no-names (including Rai, all due respect to him) and so many guys who weren't hitting the ball well in contention, you know the course is not up to the highest standards for a major.