I'm operating under the assumption that a port of Arkham Knight to Wii U is technically possible, like Arkham City and Arkham Origins before it. If it's not, then all of these points are moot.
I'm saying that if they don't make an exception for Wii U, they're shunning Wii U, artificially placing it into the "last-gen" category (despite it only being 1 1/2 years old), and they don't think it's worthy enough for a downscaled port.
That's self-evident.
Here is the argument:
I'm sure that if Wii U was exploding in popularity right now, they'd have the ability and desire to make a Wii U port happen (and forego the PS3 / 360), since they've already made Arkham City and Arkham Origins happen. That's why I consider Warner Bros.'s actions an indictment against the Wii U in particular...because they're ignoring a new console they've previously supported.
It was supported because the game already existed and was easy to cross port from PS3/360. If they are not making a last gen version you will not see a Wii U version, and that goes for any game studio. Its not a conspiracy, its not an indictment against Wii U, its common sense based on tech specs and simple business.