Because in America, not only are prison sentences VASTLY disproportionate to the crime (i.e. stacking of charges ending up with 50+ year sentences), within the first few weeks of entering the prison system, you will be SMASHED (beaten up) to see how tough you are, be forced to join a prison gang or be raped every day for the rest of your prison life as the local "Shot Caller's Prison B&^%^" or until you commit suicide. Take your pick!
When you come out you WILL be a changed person FOR THE WORSE, and unless you're 200 lbs (90 KG+) and well-muscled, YOU'RE DEAD or you WILL be crippled when and IF you finally get out !!! The guards don't (Won't) help you and the actual cell conditions and the sheer amount of aggression, savagery, disease and infection within the U.S. prison system that YOU WILL GET EXPOSED TO would UTTERLY SHOCK the average UK'er.
Look at this!
When you're FRESH FISH entering a U.S. Prison:
His other "Prison Life Videos"