I think another point that needs to be made is the fact that many local band programs have made the jump into scaled up productions since the days when DCI ruled the marching activity, and it is in this area where I think a lot of the local support has gone.
The point about drum corps having no local ties anymore is a critical one in my opinion. Parental help, local revenue streams, local businesses pitching in to directly serve their customer base and support an educational mission connected to their local schools, supporting the kids in their town, etc etc. DCI corps are never going to see that again. And in many cases, the product put out by these high school band programs surpass what drum corps put out.
It used to be that you had to go to DCI if you wanted to be the creme de la creme, now for many you can stay home and achieve it at your local school. It's still an arms race, but a more manageable one and certainly one that is closer to home for many.