Why do people continually call Skyward Sword the worst selling 3D Zelda game?

[PAOerfulone]

Personally, I think that's what makes the Zelda series so incredible and one of the best, if not THE best franchise in all of gaming.
The fact that it's able to take on and do all these different things, perspectives, and tastes, while the overarching formula that was established since the very first game of the franchise, still remains largely the same. And each and every game has been of high to extremely high quality, with every mainline console game being GotY candidates each time they come out, and Zelda Wii U will be no different.

Edit: And I don't say this just because Skyward Sword happens to be my absolute favorite video game of all time, (which I'm very proud to say it is.) I say this, because there is truth to it.
Next year will mark the 30th anniversary of the series, and it's going just as strong now, as it ever has been.
With that said, if Zelda Wii U remains Wii U exclusive, I think that may be the worst selling 3D Zelda game.
If it's also released on NX, then that could give it a chance to become the best selling 3D Zelda game (without remakes).