I think some older folks found other things to do and lost their momentum when the world closed. They didn't come back. No beginner had fun learning remote as a 6th or 7th grader so they never got the fire and quit. But I have seen some HUGE 6th grade classes this year.
Your point about the high school beast though is valid. Director burnout is real and I think it has less to do with pay or parents and more to do with hours, (self inflicted). Very few parents are begging their kid's director to go to more contests and charge more fees. That is ALL on the directors that created monsters. So a reality check and getting back to what made Texas bands great for decades was quality sound that moved. Drop all the stuff and just have great band sounds with melodies the audience can hum on their way out the gate. Go to a couple of contests in the Fall and then focus on indoor band. It worked for 100 years and made Texas some of the strongest bands in the country. Get back to that and watch the numbers skyrocket, (in my opinion).
The kids don't want all the stuff and all the time and the parents don't want all the cost. Kids want to do something with their friends. We have forgotten that in our trophy chase. Time to get back to what worked. By products include quality teachers that want to come to work (and have time for a life outside of it) and families more interested in the band thing because it isn't expensive or all consuming.