But they are, they are not allowed to leave the prison area and probably wouldn't survive the swamplands anyway. And even if there is a prison economy it would be far more static and the self-named leader of the prison would be having pretty everything under his control.
Also people there do not only get frisked, they also get abducted, tortured, killed, brain-washed and probably other stuff.
Thinking about it, the prisoner are pretty calm regarding the fact how easily they could be next?
