I think one of the problems is the smaller corps can not keep up with the money machines of the BOD' s corps.
Many years ago, I was sitting in a parking lot, waiting to play, and a Colts member walked by proud of the new G 4 valve contra the corps just got in. The next year BOD approves changing to B flat horns. As soon as a small corps gets the new toy so they can be competitive, the big corps put a new road block in the way.