Just Different Animals

Robin Hanson at Overcoming Bias went to his son's band concert.

....why do school bands play music so different from what the kids, or even their parents, choose in their free time?

As I mentioned there, popular music isn't composed for school bands, and most of it wouldn't translate well to that instrumentation even if someone wanted to try. Mind you,this isn't all bad; would you want to hear a school band version of a U2 or Beyonce song?

I recall in high school playing band arrangements of a few pop songs of the time, and most of them were pretty pale imitations. The lack of vocals was a huge factor, but the difficulty of duplicating or even reasonably simulating guitar sounds was almost as big a problem, especially for small school bands with limited resources. The only time we could come close to having the means to play many songs was when we got together will other schools for "mass band" concerts.