I don't understand some of the logic in here that somehow the Eurogamer article is wrong because a few small developers can write perfectly fine on the Wii U.
That doesn't prove the developer was lazy or incompetent, it proves what we already knew - that it CAN be done but it costs too much time and money to be worthwhile if your game is also releasing on other much easier to write on platforms.
The Wii U is not a BAD platform to develop on, that is clear, but its certainly not as easy as the competition. When you consider that even the Xbox One and PS4 now have an equal or larger install base than Wii U (and the code can easily be ported between those platforms as they are similar), its a no-brainer than the Wii U is just not third-party developer friendly, unless you are willing to commit a lot of resources to that single platform.
As many have said already, Nintendo thought they could capitalise on the popularity of the Wii and blew it.
Is the Wii U a failure? I don't think so, just as I never felt the Gamecube was a failure (and Nintendo certainly didn't, they made a profit on it). But from a multi-platform developers point of view it is and that doesn't mean they are wrong, because the most important thing for them it for the platform to be profitable and its pretty clear the Wii U so far is not, for them.
I have said it before, based on the Wii I always expected the Wii U to be a platform only really worth buying exclusives on, I always intended to get a PS4 or One for multi platform titles. The problem is that Nintendo promoted it otherwise and clearly did not support the port teams well enough to achieve that goal and then delayed their own titles so much that many of us felt ripped off.