The campers aren't there because they want to be; they're at Green Lake because they've been sent there as punishment. This isn't a holiday camp, it's a residential facility for boys who've been in trouble with the law. And as there are always plenty of boys getting into trouble of one sort or another, Green Lake can count on a steady stream of campers coming through its gates.
The conditions at Green Lake are appalling; but then, they're supposed to be. The idea is that if conditions are bad then they will act as a deterrent against any future law-breaking. But the very fact that so many boys keep coming through the gate would seem to suggest otherwise. Contrary to what the camp's sadistic administrators might think, there's no evidence that the kind of brutal regime on offer at Green Lake does anything to discourage delinquent boys from committing crime.