You’re assuming each organization spends the same on staff, which they don’t. Loyalty has legs, and instructors will go where the money is, if a better offer is made. Hence the annual end of the season staff changes. Not unusual - professional sports.
There are a handful of organizations who if they wanted to could simply spend their competitors out of business. Thankfully there are still some drum corps purest in charge who won’t accept unrealistic recommendations from their short term employees.