If you dont have to wear a school uniform do you still have rules?

I go to a school without uniforms, but there is certain clothes you can't wear, like in my school we can't wear hats or girls can't wear really short skirts. And guys can't wear really short shorts (why would they even want to?) i don't know why these rules are here because no, it does not affect education. (except I could see how the short skirt might effect it