Well, just maybe because when they are under 18 they are deemed a "child" and the thing about "children" is they don't always act in their long term best interests. They may have been raised badly. They may have done badly at primary school and been left behind by the education system. Yes, some people are feckless scroungers. But punishing them for that is leaving things too late. We need, as a society, to find ways to help people become productive members of our society, wherever they start from.
Give them an opportunity to catch up. If they don't have a high school diploma, make them get one as a condition for getting benefits. Be flexible and offer night classes for people who work part time. I agree that punishing people whom either made bad choices or found themselves in a bad situation as kids is not productive, but it is equally unproductive to leave them in the situation they are.
The alternative is punishing those who made good choices, by taxing them to pay for the others. And it's not like those choices are even hard to make: ask any 10-year-old if he thinks he might need his education to get a job. People know this. But they know they get a free ride too. That's got to change.
If I had to chose between my tax money going towards letting people sit at home and watch day time TV or letting them get an education, I'll happily choose the latter every time.
Secondly, we're talking about 16 year old kids here. If there is one thing that is pretty much universally true about teenagers it's that they're not very smart. Ask your avg. 16-18 year old high school dropout about the connection between education and jobs and they'll no doubt give you a long list of people who did perfectly fine without a high school diploma. They turn on their TVs and see people making millions without any education at all. Those are their role models. Then they look out their window and see college educated people just as unemployed as they are. Many kids don't see the connection between education as jobs. Telling people who later in life realized they might have made the wrong choice "hey you had a chance when you where a kid, too bad if you missed it", is not doing anyone any favours.
