I think there's just been pretty low interest in the final. The TV ratings were down significantly. There was also not as much media interest, articles and coverage post French Open. I think Nadal has just made it so commonplace that it's bordering being dull for general viewers.
That being said, if Novak had made the Final, things might have been different.
Nadal just lost one set at the F.O, but I think he was pretty vulnerable overall. Certainly not one of his better roads to the title. The only worse one I can recall is in 2011. He's also talked about not being sure about defending this title next year, and his Wimbledon participation is in doubt. So I don't know what's going on. People are projecting him to catch Federer, but maybe there is something else which was reflected in his game too.