Because there’s only so much money to go around and trying to educate people who don’t want to be educated is expensive. They need very small class sizes to show any improvements and you get very high staff turnover if you concentrate them because teaching apathetic students is bad but teaching hostile or violent ones is just awful.

And any kind of discipline or moving them to special classes or special schools leads to being sued.

Education is not the first or second priority in the school system or things would look quite different.

It's short sighted of course, because the money will be spent many times again over a lifetime for every botched kid. Both on the giving and receiving end of abuse.