Why do girls who play double-row keys have to wear boots?

Because when you step on the key, it is powerful.

Wear not only boots, but also flat boots. The foundation of these boots is relatively flat, the long tube of the boots can firmly wrap the legs, and the strength of stepping on the keys is relatively strong, so you don't have to worry about stepping on the keys and the shoes won't fall off.

(This is my personal analysis)