It is not the Wii U that has mildly failed, it is Mario

[gigantor21]

I think the issue is just NSMB.

A game built around mechanics from the (S)NES days isn't much of a system seller for next-gen hardware in 2012/13. A 3D Mario would've been better, as it would be a bigger draw for people who aren't diehard Mario or 2D platforming fans.