It's a bit (or a lot) of everything.
Concept: the main differentiator of the Wii U (the game pad) is not all that interesting. Whenever I consider buying a Wii U it's only for the Nintendo exclusives... never for the concept.
Price: With the concept being uninteresting, and the quality of games not being higher than PS360, the price is too high. Why would I want to pay another $300+ for the same tech I've been playing for 7 years?
Games: Wii U exclusives have taken their sweet time, and 3rd party support is gone due to the low uptake. As a PS3/360/Wii/PS4 owner, the only games I'd want to own on Wii U are Nintendo's few exclusives (but see Price).
Competition: a) You don't have a PS3/60 in which case you should certainly get one of those insteaf of Wii U, or b) you do have a PS3/60 in which case you will not feel like Wii U is enough of an upgrade - and here is the PS4 which does give a great upgrade and doesn't cost an arm and a leg.
