At my high school, stage band was the only extracurricular activity that turned a profit.
I don’t know why it would be expensive. The parents bought the instruments - the band director earned a salary but no more than any other teacher.
Football was a huge money loser.
If all the music students were buying their own instruments, or if the instruments were covered by donations, that would be a different story.
But, when the school buys the instruments, it’s expensive.
At the end of the article, the researchers are talking about funding, including funding for musical instruments.
I do agree that sports programs should be separate from the schools, too. Private leagues have teams.