I think the casual audience just isn't interested in this system.
It's not as exciting as the Wii was in 2006, and we have to remember how much things have changed since then too. In 2006, most people didn't have smartphones, touch tablets really didn't exist in the way they do now, etc.
The spending habits of this audience have just been cannibalized by the Apples and Samsungs of the world.
The other problem Nintendo really hasn't come up with a new "craze" since Wii Fit in 2007/08. Wii Music kinda fizzled and Wii Relax never even came out. Nintendo Land is the best they could come up with for the Wii U.
Just Dance has kinda come in and filled some of that void on the Wii, but why pay $350 to play that when you can just pay $30 and play it on the Wii you already have?
A game like that really doesn't make much difference whether its on Wii or Wii U.
Marketing/hype/advertising whatever only goes so far. You have to first have a product that people actually want.