I'm not speaking for anyone corp., this is just my observation. I think when the "main" corp. season ends, people do scatter. Whether its college kids going back to school, people moving to another job location (geographic), people getting involved in other activites that take the same amount of time as corp., or maybe people are just burned out from the travelling or whatever reasons they may have. My kids are part of the Crusaders out of Rochester, and they tried to get enough members together to do a parade this fall, but it just didn't pan through. It all depends on the committment of the corp. but I think parades are a great way to keep in practice musically, its great exposure as far as possible future sponsorships but mostly, I would think people would like to do it, simply for the sake of performing.
Thanks for letting me express my opinion. B)