This old chestnut. There are so many reasons why this is the case:
1. Terrible marketing- Nintendo didn't seem to know who they were marketing to. The marketing campaign was confusing at best and seemed to be a weird attempt at getting some of the PS3/360 audience whilst barely touching the consumers that made the Wii such a success. The name of WiiU was especially confusing as they made it appear as though it was simply an expansion/add-on to the original Wii.
2. Console design and hardware specs- The console itself appears to have been designed in a bubble. Whilst the likes of Sony and MS are out consulting with third-party developers, Nintendo design the console that suits them. This lead to a relatively low powered design that is only slightly better to work with than the last gen HD consoles.
3. Tablet controller- Great concept, but it's still a solution searching for a problem. The design in terms of visual marketability also make it appear to be more of a kids toy (compared to normal tablets) which further confuses consumers. It's a shame really as it's actually quite a comfortable controller. The other factor is the incredibly high cost of the controller when it's only a simple input device. That money that could have gone into other areas of the console.
4. Software- The relationship between Nintendo and third-parties is such that everyone knows the core and traditional third-party franchises will never make it to Wii U. Therefore, Nintendo has to pick up the slack and they haven't been able to do that as this is their first foray into HD development. This is where fully consulting with third-parties on design would also have been useful as they may have been able to get some advice with HD development.
5. A lot of the Wii audience moved on- Nintendo wasn't able to give them a suitable alternative so they either stopped playing games or game on tablets and mobiles. This is linked with the marketing and point 6...
6. Released late- Considering it was only a little step up from the PS3/360, the console was really late to the party when the PS3/360 had a huge list of titles. WiiU could only offer a small library with few third-party titles, many of which were only slightly improved (if at all) ports of game you could get on the older consoles. If it had released earlier, it could have gotten far more of those titles and competed with the older consoles. At the same time, the family audience found other ways to satiate their gaming thirst in tablets and mobiles.








