Drafted players are usually the very top players on the junior teams, so they end up taking faceoffs not only against other drafted players but against many who will never play professional hockey, so their faceoff win percentages end up being inflated. And even of the drafted players, fewer than half make it to the NHL, so the faceoff opposition is really far beyond what they see in junior.
If you don't want to believe me, that's OK, too.