You're not the developer, you're viewing this from the point of view of what's convenient to you. The facts are as follows: Prope redesigned the game for the Wii U because of the Wii U GamePad and Yuji Naka himself has said the Wii version of the game is the proper version. There's nothing you or I can do about that. I'm sure the reasons given are good enough: if Yuji Naka doesn't agree with the Wii U GamePad being good for motion control similar to the Wiimote, then it isn't good.
You're also forgetting that despite Wii's success, the Wii U has sold very poorly. How many Wii U owners used to have a Wii? I'm sure that the majority of the Wii owners (aka "casuals") pretty much have abandoned any and all Nintendo platforms. And if someone endured the Wii during the 7th generation,
they're likely buying a PS4 or Xbox One today. I'm positive that if Prope has decided, from a sales perspective, that making the game require an additional purchase (a Wiimote) isn't worth it, then they have the statistics and math to prove it isn't worth it. Nobody cares if you or I have a Wiimote, the other 99,998 who they want to sell the game to probably don't.