The N64 also only sold about 33 million, so we have 10 years of track record here that Nintendo has a limited audience when they follow the formula of
1.) No "once in a million" home-run type of controller hook that creates new (perhaps temporary) audiences.
2.) Same ol' third support.
Without the hook of the Wiimote, the Wii U is just a return the N64 and GameCube generations for Nintendo, except the N64 even had Rare at least which produced some huge hits like GoldenEye for Nintendo. GCN and Wii U don't have that.
It's nothing personal against Nintendo either, consumers just don't like buying entire console platforms primarily for one company's games. It's a limited market, ask yourself if you'd pay $300+ for an EA console, Capcom console, Square-Enix, console etc. with mediocre developer support outside of 6-7 main franchises.
It's actually a credit to Nintendo that they're able to basically carry their console platforms to 23-33 million in sales on their own most of the time.







