Because I didn't see the point in going back much before it was sold – this is an idea I got from Jay520’s question has Microsoft taken the casual reins from Nintendo. I am looking at trends, vs total sales. And the trend is down on both of them, but Kinect is still higher in current sales. But for Total Sales, yes, the Balance board is higher. But as you pointed out, it has been on the market twice as long.
Also, remember these numbers are inflated for the Balance Board, as many people bought the upgraded Wii Fit Plus game, who already had a Balance Board. So the balance board numbers after 2009 are exenterated.