This is ridiculous to ask.
Its like saying "Are you upset FFXV isnt coming to Wii U?"
Its simple, it just isnt powerful enough to run it and the same goes for KH3. I'd rather not have KH3's performance impacted.
I get the point about XBone never getting a KH, yet its getting KH3 and Wii U isnt, but thats simply because its powerful enough to handle it, and I pressume its happening because of Square Enix's financial problems and seeing it seems to be relatively easy and cheaper to port to both PS4/One these days, I guess they figured it was worth it. Perhaps if the two systems werent so similar architecture wise it wouldnt happen, guess it would depend on if their estimates of XBone sales exceed the cost of porting to it.
I think we should all also know by now, nintendo probably isnt going to get most 3rd party games you'd love to play on it. Whether it be down to sales, the audience who buys Wii U, or development reasons. I think it is sad, it should deserve titles at least coming to 360/PS3, but no idea about development costs porting to Wii U and whether it'd be worth it to them.
Sad, but I can think of a few reasons why devs might be put off developing for Wii U, hopefully nintendo is aiming to remedy at least one of the problems, depends if they can remedy the rest.