The Wii sold like hotcakes because of the motion control gimmick. Motion controls were a concept that absolutely anyone, from littlest tykes to the grumpiest old men, could easily understand. With a cheap price tag, it also meant that just about anyone could hop on board.
The Wii U, though, doesn't have that. It's not something that people seem to readily understand or care for. It doesn't excite people the way the Wiimote did, if they're even aware what it is at all (I still talk to people who are utterly convinced that the Wii U is just a controller add on for the original Wii). Beyond that, a lot of the casual audience that Nintendo drew to the Wii don't really care about consoles anymore; many have moved on to mobile gaming. I don't think that dropping the price tag will do much for the system, either; that's still not going to change the core issues here.
The "hardcore" crowd aren't going to flock to the system, either. Most people in that crowd aren't going to care about the touchpad controller (if anything, some will see it as a detriment). Sony and Microsoft's systems are much more powerful and more designed like PC's, which means that the current triple entente of multiplats (PC/Xbox/PS) will be even more solidified. Porting a title over to the Wii U is going to require a lot more effort, time, and money from developers, which means that most developers will likely opt not to, which means that Nintendo's dearth of third party support is going to persist. That's going to keep a whole lot of people away.
Nintendo will produce Nintendo games, of course, so Nintendo fans will likely have all they need. Once they see the title they've been holding out for (A new Mario Kart or Zelda or what-have-you), they'll hop on board. That'll keep the system afloat, sure, but it won't carry the system to victory.
Personally, I think we're looking at another Gamecube here - it'll manage a marginal profit in the long run and subsist on the dedicated fandom already in place while their handheld division picks up the slack.