The Wii U game uses the touchpad controls from the 3DS version, which is a different game. Let's say they had to use the gamepad, then it makes sense to use the 3DS assets, since it fits the game on the Wii U. Because the game was so heavily modified during the port to the 3DS, the Wii components no longer fit in with the game, so, the Wii U version used the 3DS assets.
That's my guess, at least. Considering the Wii U also drops to 30 FPS throughout a lot of the stages... I'm not entirely sure if it isn't performance related too.
That's my guess, at least. Considering the Wii U also drops to 30 FPS throughout a lot of the stages... I'm not entirely sure if it isn't performance related too.