Nobody asked for a successor to the Wii. There lies the problem with Wii U. The vast majority of Wii players moved on to tablets and phones. Another group, though not as large, got into PS360. The true Nintendo loyalists are the ones who bought Wii U at launch, and of course not all 100% of them got it. Nintendo may just be realizing they made a new console for an audience that doesn't exist.
The whole "the casuals have all moved onto tablets/phones" thing is a myth; yes, the audience had shrunk, but Just Dance 4 selling over 5 million on Wii since the end of last year shows there's still an audience for casual games on consoles. Problem is, the Wii U's out of their price range at present. Casuals gravitate towards cheaper consoles, and the Wii U is currently the most expensive on the market.
I dont think that is a Myth infact its one of the reason. Wii practically opened up casual market in 2006 with its ease of play and mobile phones and tablets were no were in the picture. Lack of hardcore games for wii drove away the hardcore gamers like me to a PS3, just so that they can cater the casual gamers and their need, and when the Facebook/mobile/tablet dominance hit the full swing majority of the wii casual market went on to the multiple purpose device which offered more than wii itself and could be upgraded every year with different OS to choose from. For a Short time MS did bring back those casual audience to console once again with Kinect. but wasnt enough as mobile and tablet have been evolving at a rapid pace for any gaming console to keep up.
Now with Wii U Nintendo is targeting again at those casual market (who are happy with their SP/tablet)and also trying to cater the hardcore gamers, who by now already have a x360/ps3 a smartphone/tablet. so why would I (once a Nintendo buyer) would wanna buy a game console that i already have. Instead i would wait for PS4 which i assume be a significant upgrade over PS3. And also I dont see any exciting games releasing on Wii U untill PS4 is launched. In fact I have a PS3 which has exclusive coming up like gow, tlou, beyond and multiplats which will be available on Wii U too with almost identical graphics.
So in theory, Wii U isnt offering me anything that PS3/360 doesnt offer.