The WiiU didn't "underperform". It's selling right in line with the trend Nintendo's home consoles have taken since they first entered the console market.
NES: 62 million
SNES: 49 million
N64: 33 million
Gamecube: 22 million
WiiU: 13 million
The Wii is an outlier. It rode the wave of the "blue ocean" and motion control fad and stepped away from the "traditional" Nintendo console. When Nintendo went back to a more standard console with the WiiU, they fell right back in line to the trend they had: declining console sales. They didn't have a gimmick (motion) this time around. They had to rely on the strength of their library's reach to the consumer (not a gimmick) and the trend is that that reach has been dwindling since Nintendo became a console maker.
I'd even be willing to bet that the Wii, on its library alone with a traditional controller, would have sold less than the Gamecube. I mean, think about it: what's so different about it from the N64 and GCN before it, and WiiU now? Wii has Galaxy, N64 has SM64, GCN has Sunshine, WiiU has Mario Bros U. Wii hasBrawl, N64 has OG Smash, GCN has Melee, WiiU has Smash U. Wii had Twilight Princess, N64 has Ocarina of Time, GCN has Wind Waker, WiiU has Breath of the Wild upcoming. Wii has MKWii, N64 has MK64, GCN has Double Dash, WiiU has MK8. Wii has DKC Returns, N64 has DK64, WiiU has Tropical Freeze. I could go on.
These are the core games that sell Nintendo consoles, alongside an allotment of random 3rd party games. So, why did the Wii sell 100 million, if not for waggle, when the other Nintendo consoles sold so poorly? It's abudantly clear that the fluke of motion control is why. When that fad died, Wii sales fell off a cliff and Nintendo quickly said "gotta move to the next gen now", because the Wii's library wasn't what was selling the console. It would have continued to sell well if the library was indicative of a 100 million selling console. When it's the games' library that's really strong and leads to those kinds of sales, they don't just disappear overnight like Wii sales did. After 4 years, the PS3 and 360 still sold consistently, for example.
So, to bring it full circle again, the WiiU isn't underperforming. Get rid of the flukey sales of motion controls and Nintendo is right where they ought to be, following historical data. When people say Nintendo should pull out of the console business and go 3rd party (they could still do handhelds), it's not to spite Nintendo. It's because they realize that things have been all downhill for them since they entered the business, and aren't thrown off by the "accident" of the Wii, considering that that success won't be repeated by them and them doing tried and true traditional consoles ain't gonna work.
