Why do Japanese female students wear short skirts in winter? Because it cannot be rolled up any shorter.
The length of the skirts is what girls fight for in junior high and high school. The shorter you get to wear it, the higher you are recognized in the school hierarchy system. What after-school club you belong to adds an extra layer to it - at my school, girls in the cheerleading club reigned at the top.
Through the way we wore skirts, we were quietly communicating our social status. Wearing it “wrong” thus could get us in trouble.
Here are some of the risks girls at my school had to take for their survival.
If you cut your skirt short, your teachers will send you to the faculty room for your ignorance of the school rule. If you wear shorter than your upperclassmen, they will send you to the back of your school for your (unintended) arrogance. If you keep it as long as it originally is, your classmates will send you to a corner of the classroom with the label “that nerdy girl”. We had to develop thicker skin (literally) to survive in the cold school community.