The worst sorts of 'sports day' aren't 'sports' days anyway, they're 'running races' days, and lots of people suck at that.
But it is relatively easy to organise of course.
If sports days involved a number of sports, and kids could pick or be selected from earlier heats.. OR they could pick to be involved in organisation, refreshments, set up...
I'd be all for that - those who enjoy running can run, those who are good at or enjoy throwing can throw, those who hate every second of sports can still be involved and do something else. Great.
But forcing kids to do things they're awful at or really hate... in front of the whole school. No that doesn't teach anything useful at all. Kids already have to do loads of things they don't like (I mean, GO to school for a start!). Adding 'public spectacle' isn't beneficial.
I wasn't shit at all sports when I was at school - I could ride, I could do archery, I could throw and catch well, I climbed, I skied, I canoed, I swam very well, I dived well...
I could not run. Sports day was.. running day. Thats it, that is all. Nothing else.
So i went through primary and then secondary with a label of 'is bad at sports' - when in fact not only was I not bad at sports I probably did MORE sports activities during evenings and weekends than the fast running kids at school did all bloody year.
Doesn't matter though does it.. because that public humiliation of wheezing in last with a twisted ankle gasssssssping for breath AGAIN in front of 1000 of your peers... that wipes out the value of anything you did out of school when you're somewhere between 5 and 16.