The Plains were located near the hole in the Shield Wall created by atomics used by the Fremen. Once the Sardaukar deployed on the Plains; they were vulnerable to the Sandworm riding Fremen who easily defeated them.
A real world comparison may be drawn to British General James Wolfe's defeat of the Marquis de Montcalm outside Quebec, Canada. Wolfe used the Plains of Abraham to lure the French and Indian armies out into the open where they were forced to fight a European style of battle. Wolfe's redcoats triumphed over the French/Indian army by drawing them into a fight of Wolfe's choosing, instead of the 'Hit and Run' tactics used in that area in that era.