I suspect few Americans realize just how much of an outlier the US is when it comes to incarceration rates. More than half a percent of Americans are currently in jail. Why? The "war on drugs."
In my eyes it's very simple: a commercial prison system in need of cheap labour, with enough clout to start and maintain the "war on drugs". If you have enough money, you can buy your way out.
In effect it's the same as slavery: only the source of the work-force is different.