You have to consider this...
Every scammer either a) Starts scamming again under another alias or b) quits altogether and becomes legit.
Any of these guys who left their books probably could have taken enough cash with them to live for a while retired... But I'm sure eventually they'll get that bug again.
Think of how hard it is for these guys sitting there in their living room knowing that they could start back up with a clean slate (no debt, new customers, etc). Why wouldn't they?
I would... If I were that type of person.