Didn't do that while!? WW sold 4.6m on instal base of 22m, that's attach rate of around 20% attach rate! In what universe is that "didn't do that well"!? Thats much higher attach rate than TP on Wii, not to mention TP on GC. Skyward Sword would definitely had better sales if did not come when Wii was dead and if didn't required addon or different controller.
Splatoon, Mario Kart, Nintendoland, Smash, Mario Maker, 3d Wörld, New Super Mario U
All did better on wii u compared to Windwaker on GC.
The thing is, people want NX to be a gamecube 2. A tradional gaming console with high power as direct competition to ps4&xbox one. That would be the only reason to bring zelda to nx. Such a console will fail. Like the gamcube failed. Zelda wont help anything. The Wii U had much more popular games then any zelda (if you compare attachment rate) and failed horrible nontheless.
Nintendo Land was bundled with every second Wii U console, NSMBU also had great number of bundles, Mario Maker didnt sell better than WW. Zelda was never seller like Mario, Mario Kart or Smash and now Splatoon game that have huge mass appealing, so fact that those game sold better than WW doesn't mean that WW didnt do that well.
Wii U had multiply reasons why failed, one of those reasons was very weak launch titles and software drouth, Zelda U port for NX will be very strong launch title especially in combination with probably new 3D Mario game.
Again, with Zelda U port on NX Nintendo will have very strong launch title and they will sell several millions of copies of that game on NX alone. Only thing you can say is "Wii U will not have exclusive Zelda game", but nobody cares about that because that don't change anything, Wii U owners will still get game, fact that isnt exclusive dont change nothing espacily in era where evre second game have some kind of a port or reamaster.