There are a lot of different factors at play here, to be honest.
The absolute log-jam of titles on smart-phones and tablets has definitely hurt some games. There are probably dozens of "brain training" games out there for cheap, for example. Genres like this, where a casual gamer doesn't have to buy new hardware, will bleed away sales from dedicated gaming consoles.
As far as the Wii U goes, I've been saying for years now that we will not see a casual craze like the Wii in back-to-back generations. It was simply never going to happen, even if Nintendo had released the "Wii 2". Many of those who bought the Wii were not gamers, they were just fish following the current. They bought the games, played them for a little while, then stopped. That's nothing against the Wii, that's just a result of the Wii becoming the center of a viral fad. The people I'm talking about bought a console they can pull out now-and-then for parties and, essentially, they're set. They will not be buying another console for a long, long time, if ever. We all probably know one or two people personally who fit this description.
That's why I've been saying all along that Nintendo fans should consider the Wii an anomaly and not judge the Wii U against it. A typical Nintendo console, assuming it does not see significant third party support, should likely have a baseline closer to Game Cube levels, as they typically lack software support for several popular genres. Gaming tastes have expanded greatly but Nintendo has decided to concentrate on a few genres in particular, like platformers, which makes Nintendo consoles somewhat niche unless the difference is made up by third party developers.
Basically, that "blue ocean" has turned into a "red sea" thanks to saturation from mobile games and a possible consumer base which has shrunk compared to Wii levels.
