I'm quite sure that all corps only receive the rights to arrange the music they play for competitive shows and for official corps or DCI recordings. BD and SCV obviously feel that they have a responsibility to themselves and to the owners and legal distributors of the music to prevent it being shown for free on YouTube. Other corps perhaps have different concerns.
Brass warm-ups or percussion warm-ups that are merely exercises and are not copyrighted are a different story.
I, too, miss seeing the shows for free, but the corps would certainly seem to be within their rights.