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The Wii going viral with casuals was an anomaly that isn't going to happen in back-to-back generations. They bought the console in droves, yes, but most of them were pretty much done with console gaming after that. I'm not saying the Wii collected dust necessarily, though it did for a lot of them, but rather that most of them bought it specifically for a few games. Wii Sports, Zumba, Just Dance, and maybe a couple of others. The majority of those people aren't interested in upgrading video-game consoles every few years. They break it out when friends are over but it's not something they're invested in as a hobby.
Nintendo has the numbers, they have trend analysis and charts of everything, I'm sure. They know a lot of the Wii sales were fad sales that won't come back. They rode the train then jumped off before it ran out of track. Now they're back to the audience that is a constant, the core gamers who actually are invested in gaming as a hobby. Sure, they want whatever casual sales will come, but they know they can't live off those alone, not this time around.
My niece was telling me about how good she is at Zumba the other day. It beats me what she was talking about, to be honest, but I did ask her if she was interested in the Wii U. Her response was, "nah". That's it, just "nah". She has her Zumba and that's enough. I think the same is true for a lot of the casual market.
