I was never a band director, but I later in life I did have a friend who was slightly older than I and a former band director. Never got around to the kick-back question, but we did discuss cornets falling out of fashion. He blamed the music stores. He said that when he started most music stores provided cornets for lease/purchase. So you ended up mostly cornet players and you hoped for a couple of trumpet players to "balance the sound" (his words not mine). Eventually, the music stores started pushing trumpets and eventually quit offering cornets at all. On a secondary note--I have a very good friend who owns a music store in the midwest--he told me that the better high school bands in his area have started providing professional level cornets (usually Yamaha) for their top trumpet players to play during Concert Season. Both these stories are from the Mid-West--the first from the early 70s the later is current--so maybe the cornet isn't as far gone as it might seem.