The problem with the Wii U has been a differentiator one from day one.
Most of what is being released on it by Nintendo are products that have already been made on prior consoles. Only with better visuals. It needs something fresh. Something game changer. The gamepad has a lot of potential, yet Nintendo is playing it safe by releasing Wii U versions of games everyone played on the Wii not so long ago.
If that were true, then why is the PS4 selling well? In terms of gameplay and controls, the PS4 and it's games do nothing new, all it has is better visuals.