Each "investor" in a Ponzi scheme has smaller chance of return than the previous one.
Everybody who knows what a Ponzi scheme is and plays, actually hopes that he will not be the scammed one, he hopes he will scam the next "investor".


Unlike a dice game, where you know (if the owner is fair) that you will surely be paid if you win, in a Ponzi, even if the owner is fair and doesn't run with the money, at some point the game will stop and the last ones "playing" or "investing" will lose.
At that point the owner of the game will publicly called a scammer anyway. And because that, most will actually wait for the best moment and just run with the money. Because scammer with money is better than "fair" scammer, you know.

I hope it make sense now.