Ground fighting is part of the Krav Maga training. Add the Krav Maga stick defenses and you get a ground defense against a stick technique. Of course this is not a common situation, but you know Krav Maga, we wanna be prepared for all situtations. And the most probabilistic reason why this one could occur was if you attacked by a person with a stick and you fell on the ground. Being attacked while on the ground is not the best thing that can happen to you, stick or not.