Some of it has to do with the fact that the TV picture is scanned; it's not "all there" at the same time and the camera is taking one instant in time, so you'll get scan bars representing what that picture "really looks like" at that fraction of a second. Sort of like looking through your fingers while waving your hand back and forth in front of a TV. The retentivity of the eye keeps the frames of movies or TV long enough so the frames blend into action. Also cameras are designed to take pictures mostly in daylight and the TV phospors don't produce that same sort of light. Not a very scientific explanation, I fear!
