In short - They chose to spread mental illnesses instead of containing them on the prefectural level. Some schools made their uniforms gender-choice based and only for girls. It was done not for practical reasons. Boys were not given the option to choose, yet.

https://soranews24.com/2020/12/23/japanese-school-renames-boys-girls-uniforms-as-type-i-and-type-ii-in-gender-identity-reform/

Diversity anybody?