With Donkey Kong Country: Tropical Freeze coming to the Nintendo Switch, Nintendo has taken some unusual steps. The game has been delisted from the Wii U eShop in advance of the launch on Switch.
The game can no longer be searched for on the eShop, or be purchased on the NoA Website. That being said, the digital version is still available at retailers like Amazon,
There is speculation that this is due to the game being cheaper on the Wii U, but is just speculation at this point and there is no explanation at this time from Nintendo. We will keep you updated.
Source: Wii U eShop