Okay, here is the "for Dummies" version:
Motion controls when they were first introduced for the Wii back in 2006, was targeting not the traditional gaming audience. During the E3 when they unveiled the Wii, it was either Reggie or Miyamoto that said that something along the lines of, "for those who have never picked up a controller..." That statement was intended for, what the hardcore called at the time, "casual" gamers to pick up and play the Wii because of the ease of use and low entry barrier into gaming.
Sony first tried to copy Wii-style motion controls with the SIXAXIS. The only title to make a considerable effort to utilize it, Heavenly Sword, failed to capitalize despite the media's praise. All games since Heavenly Sword, with the exception of Metal Gear Solid 4, have completely dropped SIXAXIS support.
At E3 2009, Sony came back with the Playstation Move. To be honest, it is a complete rip off of the Wiimote with one notable exception, there is a ball on top of Sony's remote that changes color. It eventually launched alongside the PS3 Slim.
The Kinect was also announced at E3 2009 and launched the following year. However, unlike Sony, Microsoft is expanding the Kinect to include a Windows 7 version.
The problem? Both target casual gamers who would like a relaxing spin at their favorite sport rather than their base. IGN put it best during the review of the Kinect device itself, "Kinect can be a tremendous amount of fun for casual players, and the creative, controller-free concept is undeniably appealing".
There is always two levels to gaming, casual and hardcore. Motion control just added another barrier to that gap.