Because its huge hype is better served as NX momentum.
Look at this Polygon vid:
Can you feel the power? It is called a Phenomenom. Supposedly something of this magnitude haven't happened at E3 since the Wii. Why waste this hype on a struggling late console that even one of it's top devs admitted didn't worked as they hoped? Sacrifice the WiiU for the better of the NX.
Edit1: Consumer confidence might be hurt a bit... but not really. This game's hype is way bigger than the resulting dissapointment from delaying the WiiU version or even cancelling it.
“Simple minds have always confused great honesty with great rudeness.” - Sherlock Holmes, Elementary (2013).
"Did you guys expected some actual rational fact-based reasoning? ...you should already know I'm all about BS and fraudulence." - FunFan, VGchartz (2016)