I love it when gamers don't understand business: Nintendo released the WiiU for the sake of turning a profit and their biggest money maker is through software sales. The WiiU was not released to outsell a console that suffered from piracy.
Because if they cut and run now, they can't recoup any of the losses they incurred in the last few years of 3DS/Wii U. If they keep Wii U on the market and act to maximise profitability rather than marketshare, they can rescue some kind of financial positive from what is otherwise a poor generation for them. Launching a new console will be expensive, as would going third party. Better to make what money they can before they have to sink even more money into a change of direction.
What looks better to a consumer buying the next home console from Nintendo? Nintendo, the platform holder who couldn't make Wii U succeed so they dropped support within three years of launch (and who cut the 3DS price massively after launch)?Or, Nintendo the platform holder that continued to bring their biggest, best titles to Wii U despite a small userbase?
What's a better bet for publishers and consumers? A platform holder who stands by their hardware, or a platform holder who runs at the first signs of trouble? If publishers and consumers are going to invest in new Nintendo hardware, Nintendo's decision to stick by or drop Wii U prematurely will play a major part in how well their next system does, at least initially. There are a lot of other factors Nintendo will need to nail, but sticking by Wii U and grinding out profit is far more sensible than dropping the system prematurely.