You may be thinking of the knot moving to the right. It is fixed and can only move up or down vertically. Not left or right.
As such it has to move with the up and down motion of the rope at that point.
If the knot was a cork floating on the surface of a pond and a water wave was approaching from the left as shown, which way would the cork move?
The next part of the wave to reach the cork or knot is below the mean level. Not above.