Because, from the sound of it, Nintendo totally loves them. While developing The Legend of Zelda: Skyward Sword, Nintendo's Eiji Aonuma thought about ditching the Wii Motion Plus controls. Now, he wouldn't have it any other way.
"I honestly think we cannot go back to button controls now, so I think that these controls will be used in future Zelda titles, too," Aonuma told The Official Nintendo Magazine.
This should delight players who enjoyed the motion controls in Skyward Sword. With the Wii U, it should be interesting to see how Nintendo will implement motion.
The one-to-one motion controls did add to things like Skyward Sword's archery experience, but some didn't find the sword swinging as compelling with motion controls—or better than old fashioned button pressing.
Nintendo usually does an excellent job of marrying its hardware with its software, so chances are, it will be well done.
That being said, no more button pressing? *insert sad face*
Be sure to read Kotaku review of Skyward Sword.