Why it was canceled is actually quite simple. The demand for the DLC content by owners of the Wii U version of Batman: Arkham Origins is simply not strong enough to support its release, according to the powers that be at Warner Bros Interactive Entertainment.
The story campaign was one of the star attractions of the Wii U five-part Season Pass for the Wii U version of the game. Nintendo will be refunding those that purchased the Wii U Season Pass, but no timeline was given as to when this might happen.
The Wii U received a special Armored Edition of Batman: Arkham City when the console was released that included a number of special additions to support the unique hardware of the Wii. Warner followed that up with the release of Batman: Arkham Origins. Neither of the titles has sold that well on the Wii U, while the releases on other platforms have done well. So, the news really comes as little surprise. as software publishers continue to choose not to release titles for the Wii U.