Because staying at home starring at a television screen is better then going for a jog. Its another stupid gimmick which in the end is going to kill the Wii.
I would not purchase any sort of replacement parts from DX.
I've gotten a PSP button set that doesn't work. A DSL screen that doesnt' fit snugly in the socket (to where I have to add extra material so it will stay put), and of course the aforementioned shoddy case.