I know a number of people who did it when younger, and some that work for Corps now.
I marched at the end of HS (I played FB at the beginning; Knee 2.0 isn't as good as Knee 1.0, and Mom wasn't happy, so...) and in College, but I never got the DC appeal. Maybe because I liked having spending money and didn't enjoy long bus rides across the country. (Caveat: I can* play trumpet, so I could have done it...)
I -do- appreciate the skill that goes into it, and the attention to detail. That has always been the biggest beef I have with bands - Dress your lines, dumbasses, it's easy, and the little things really count.
I've got to get the Sax down... Homecoming is in a couple weeks, and us old-timers get out an do what we can with the kids. And playing once a year isn't good for your skillz.
*-'Could' is probably a better term. I gave the Trumpet to my Cousin a couple decades ago, and my attempt at Taps on my Bugle the other day did not go terribly well.