Or prehaps its because by and large Norwegians didn't mind the Personal union under Denmark, as it wasn't by the nobles seen as an uneven union (sure, Denmark was undoubtly in the drivers seat, but it was not nearly as imbalanced as the British Union, and the majority of Norwegian nobles were actually Danish, as their noblity damn near went extinct by the Black Death). And that there was a constant concern about what Sweden would do the second they tried to (or managed to) gain independence ... rightfully so seeing as Sweden invaded and conquered Norway when they tried declaring indepedence following Concert of Vienna.
Denmark-Norway might well be one of the least volatile personal unions in Europe.