Metallicube on 22 April 2013
It's not a marketing problem, but a game problem. There still aren't many games for Wii U, and the few there are are either ports, or tend to appeal to the same hardcore Nintendo fan niche that bought the Gamecube, with the exception of NSMB U, and Monster Hunter in Japan. When the games come, so will the consumers.
The controller I feel is also a piece of the problem, as it doesn't have the same appeal the Wiimote had and is trickier to use for the average consumer, but if there are enough quality games, that will no longer matter.
