And most likely they didn't even teach you the rules.
We played football, not to an insane degree, but I always found it weird that they assumed everyone knew the rules.
Personally I don't think gym and music should exist at part of the school day, at least not in larger cities. Instead it should be required that everyone takes lessons in at least one instrument, and practice at least one organised sport after school. Then children are free to pick something they care about. Any fees should be paid by the city or government.
This would be nice in theory, but most organized sports are seasonal with the majority occurring over the summer break. They'd need to subsidize for year long programs, and that doesn't seem financially feasible.
Also, certain sports cost more than others, so certain families getting more money because their child picked a more expensive sport doesn't seem fair.
I grew up in Australia where it was assumed that everyone automatically knew the rules to every sport. I fumbled my way through cricket and soccer for years. I tried finding books in the library that would teach me the rules, but couldn’t. Still don’t know how to play either of them.
And one of the methods to do that is to expose kids to a variety of sports so that they'll hopefully find one they like. You might not like volleyball but for someone else in the class that forced participation might be the start of a lifelong love of it.
Also, I'm glad I learned the basics of tennis, soccer, baseball, flag football, volleyball, table tennis, badminton, archery, and so much more in school. I don't play any of them frequently, but when they do come up (like as a social activity at a company offsite, or a leisure activity when vacationing with friends), it's nice to be able to actually do them.
And thus the reason I even enjoyed badminton. I thought it was dumb and I'd hate it. Turns out it was fun. Probably haven't played it since high school though... All well. Maybe when I have kids, lol!
"I don't wanna play volleyball, can I get some guys and we'll play floor hockey instead?"
"NO"
Well, fuck gym I guess.