pff, there was some movie long ago, some technician was installing a few 1-armed-bandits in some pub, and asked the owner - should they give 1 win per 100, or 1 per 1000 ? And the owner answered: What? 1 per 1000? We're not a charity here, there must be zero wins!
Sometimes all hell breaks loose and multiple or all machines pay out. The joke is that most gamblers won't cash out and go home - they will "reinvest" their entire win in hope to win more... and the really desperate ones throw even more "fresh" money at them.