Because they're children and children grow up to be adults and there is no reason they should choose to turn to crime because they got neither a standard education nor vocational training along with the expected education.
That's called the school-to-prison pipeline.
Vocational training is important- not everyone is cut out for college -but formal education is important for every child- the lack of it is what we're seeing play out in politics today. And Civics should be stressed from the first year in school. Everyone should be taught why being a good citizen, and a critical thinker, is a duty we all owe to society.
And, as citizens, we owe it to ourselves and to society, to educate every child, either to go on to higher learning or to be literate and a tradesman if learning a trade is what works best for the child in question.