I'm not a physicist or in any way educated about physics, but I can have an uneducated guess.
When the kinetic energy travelling backwards and forwards through the cradle begin to lessen significantly, maybe it becomes less of a striking action and more of a pushing motion. Sort of like when you're playing pool and the difference between jabbing the ball and pushing the ball along with your pool cue.
Once again, I'm probably wrong but it's a guess nonetheless.