Can an opponent folding make you go from probable winner to probable loser?
Suppose the five community cards wind up being 9♦, 10♥, 10♣, J♠, and 3♠. Then C would win with a better full house than A, but A's full house is better than B's pair of 10's. Before C folds, this would count towards his 25% win chance; after he folds it counts for A's 56%. When C folds, we're essentially taking his 25% chance to win, and splitting it up between the two remaining players. The issue then becomes that the cards that help C out also help A more than they help B, so most of C's 25% goes to A rather than B after C folds.