That would be one of the possible solutions for repeat offenders.

As to the why. Kids are not raised with a parent in the home or in a community with like-minded people so, there is no guidance, expectation, or consistency. Kids that are not brought up with consistent moral values go wild. Also kids that are from neglectful and/or abusive homes don't have the resources available to them to stem the behaviour before it gets out of hand. That is my two cents worth.

If it’s anything like it is in America then teenagers and young adults have always been complete dicks to everyone. The one thing that changes it is the probability of having an Ok future if you keep your nose clean.
Aggressive teenagers aren’t limited to any socioeconomic group. They’re like that until they understand consequences, so show some early, strongly and consistently.
The rich kids were the bullies in my school.
The threat of messing up their permanent school record was all that held them back.
The really rural kids just had nothing to lose and I know at least 3 murder victims and their murderer is in a small group of kids that rode on my school bus. But which one? I hated being anywhere around them so I didn’t know them well enough to know who, unless they all participated. The police just declared them missing, but their bodies were in the river and I knew it all along. They found some of one kid’s possessions on the Chuctahatchee river like three years later and declared him drown.
That all happened in 1973.
Out of control teenagers are an absolute menace.

This behavior isn't new, just the ability to have it documented and publicized. The aggressors ran rampant in my school and while I tried to avoid them, I eventually ended up being badly assaulted. They were the rural kids @Willow_Wisp mentioned and they had no fear of punishment because they never were ... they were the aggressive, loud, and obnoxious white guys who got away with everything, and fear of their retaliation made me beg my parents not to complain to the school. Instead, they got me out of that environment by moving me to a private school, but that's not an option everyone has.

I'm not sure moving them into the military where they can continue their abuse in another setting which rewards aggression is really the answer. As with most things, there is no one solution, but a combination of changes in the power structure of society, better controls within places like schools, and enforced socialization in the form of therapy for kids acting out aggressively would be a good start.

@Lauren The military has ways of disposing of their psychotics. In war and other means.
The worst bullies become captains of industry, leaders of countries and are the economic cabal.

I think a total reset would be more effective. Punishment seems to exacerbate the problem, it is seen as a proof of a superior person that does as it pleases and society cannot stop it..

@Kurtn You may be right for repeat offenders/die hard bullies but if you can catch them in the beginning of their bullying careers, then you may just get some that will change their ways. If counselling and mentorships are included then the percentage just might increase. I think it is worth a try at least.

@Betty Back in the 1800's in Brisbane, they had the same problem with miscreant youths. The solution was to pack the offenders off to a wilderness area where they were controlled in that could not leave the area. For the rest, food water , shelter they had to fend for themselves.
History shows that some of the most diligent farmers, workers and community leaders spent years in the area that is now the Bayside suburbs of Brisbane.
Through brutal hardship they learned to work together, rely on each other, adapt to changing times and strangely enough learned discipline.
Something like that would never happen in our present politically correct and holier that thou society. .

@Kurtn Society has changed a lot since then. Some changes for the better and some not. It is also well know that abusers of all kinds search for target rich environments. We are well aware that finances and profit margins dictate labour costs and when low wages are offered there is usually no background checks made. In my opinion I don't think it would work out well.