This guy got away with it for 5 years. The only other one I know of is the McDonald's Monopoly guy who rigged it for 4 years. This tells me you can get away with it for a while, repeatedly. And I really doubt most people would take a huge payout, then keep working that job to do it again. So I suspect that it takes 4 or 5 years to get caught and we're just catching the minority of people greedy enough to keep their scam going for years, despite the massive amounts of money they've accumulated already.