The casino operators need to think about the law of large numbers. If you have an edge, what you want is for a bunch of little guys to bet against you. Your certainty of winning against a million little bets is enormous, if you have an edge. And you do, because those games are made that way. What you don't want to do is bet a few big bets. You might be smarter than me at guessing the outcome of an election, or a coin…
The problem is there's a really uneven distribution. They probably get 50% of the wagers from 1% of the gamblers. But they still have enough whales that they rarely have a losing day.