I'm gonna try to go deeper in your question.
If we think about SWOT analysis, i would say that Nintendo played their strengths and weaknesses (internal factors) all wrong, and at the same time all threats (external factors) took place. There is also the fact that Nintendo decided to go on a very risky way by betting on an expensive gamepad, and when you take that much risk then the results will be either a jackpot or a big flop.
By threats coming true i mean third party crap job as an example. The little support they gave were faulty from the start and a lot of games didn't made there, despite having PowerPC versions of them at the PS3 (I suppose the architecture would not be a problem because of this, but i could be wrong, i know little of programming). Even worst, most companies stated a lot of BS as reasons for not giving WiiU games, instead of just saying they didn't believe in the return of the investments. An example of this is EA saying Frostbite 3 engine couln't run on WiiU, and then backtracking on their words months after.
Despite that, if only external factors were hurting, Wii U would be selling better than GameCube. Nintendo did some very wrong marketing decisions and misjudged the difficulty of jumping to HD, causing a drought of the first party titles that usually carry their consoles to profitability point.
