Society tells us what is accepted and appropriate for men and women to wear, and this feeds into gender "norms." We're told skirts are feminine, and if males want to wear them, it's a threat to their masculinity.
Even if the skirts are just more practical. But as a society and culture, we've been fighting these gender norms for years.
It's a very exciting time we live in, where a peaceful protest can be formed by teenage boys. They make up a demographic that gets a lot of flack for being immature and annoying (let's be honest, we've all babysat them and have horror stories), but what these boys did was downright inspirational.