Because gamblers doesn't want to disclosed the amount that they have lost, so you can only hear from them, that they won this amount, but how much money they have as capital in order to win?
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It is a peculiarity of human psychology to hide one's weaknesses (in this case, gambling losses) and to exaggerate achievements (winnings). It's funny that this works in favor of the casino, because for people unfamiliar with this topic, from the outside it seems that earnings here are guaranteed for almost everyone, you just need to make a little effort or just be lucky. Thus, attraction to this area works very strongly even without much effort from the casino.