Bill ended up ADDING 100,000 to the pot at the very end. With only two other contestants left, it's only natural to assume that both know you're the mole, so why continue trying to be a "player"?

At that point Bill knew the girls knew he was the mole so I think he decided to give whoever wins a little gift, if that makes any sense. Sort of like Kathryn trying to help out the guys in the final mission knowing they had her pegged as the mole.