Now, please understand, I am a trombone player AND a Cadet alum (euphonium). Obviously trombones were not allowed because prior to 2000 DCI marched bugles keyed in G. Now that they are B flat or whatever else they want, there is really no reason for not having trombones. Except for the fact that they just wouldnt work. Sound wise or visual wise. Believe me, it's hard enough marching some cadet drill with a euphonium sticking a foot and a half in front of your face. Imagine a foot more out there.. or more. There would be broken horns and a lot of hurt people. Thats just my opinion.