He could, but as long as he had all the slips of paper, he can't but gain by going back on the commitment not to trade below a certain split. He can only deal once with each person, so with the same number of slips and co-players, everyone dealing with him knows there's no substantial chance he'll wind up not trading with them at all as long as they're willing to give him a penny of the dollar. As much of the dollar that slip represents as they're willing to hold out for already belongs to them - since if he doesn't use it, he gets nothing, and if he does, he gets some non-zero amount. Only by taking away his own option to use the last slip does there come to be any credible chance that somebody doesn't get to split a buck with him.

Tearing up two slips would likely have lost him the game, however, since the actual winner had obtained over five dollars, and one couldn't manage that with only five slips.