Reason being is that the sweetspot is the center of the club portion that strikes the ball, not the hosel. Does that make sense? Now it does appear to the eye that when you rotate the club during the golf swing it might appear as the face is opening and closing around the hosel. But you are not directing the hosel you are directing the sweetspot. This the longitudal center of gravity line which you can see but exists and the forces applied to the club recogize it.