Why can’t boys wear skirts?

No one says it’s impossible.

There are not many men in the world's ethnic minorities who wear skirts. For example, Yemeni men wear short skirts, Tuta men in southern India also wear aprons, Iroquois men wear deerskin short skirts, and Hopi men wear short skirts. Men wear white cotton skirts, Thai men in Myanmar and Thailand wear uniform skirts, Scottish men in the UK like to wear plaid skirts, etc. In South Pacific countries such as Samoa and Fiji, men generally wear skirts. Some Dai men among my country's ethnic minorities also wear skirts.

It's just that we are all used to men not wearing skirts. If you do, others will laugh at you and think you are a pervert, a gay or a shemale. Even if you are physically and mentally healthy, outsiders won't see it that way. People will only see the superficial ones, so it is recommended not to wear them.