I have two possible explanations:
1) The Wii U costs more to develop. You've got a far more advanced controller in the gamepad compared to the xbox and playstation controllers.
2) Nintendo knows they have lost this generation, so at this point it is about having as much profit as possible. What's the point of taking losses on a device to push out systems this late into it's life cycle with this much failure so far? Sony and Microsoft are trying to push systems, so they are either taking losses or taking less profit than they could on their devices to increase market share. I don't Nintendo cares about market share with the Wii U, but rather is focused on the NX getting good market share, so they want to waste as little money as possible on the Wii U going forward.
