Why do you think the gamemakers decide to change the rule for the Hunger Games

They wonder why nobody is ending the game when Claudius Templesmith's voice booms over the plain, announcing that the dual victor rule is no longer being honored. Peeta insists Katniss kill him, but she can't handle the idea. Suddenly, a stray comment of Peeta's about how the game has to have a victor gives her an idea. She realizes that audiences would revolt if their game had no victor, and perhaps the Gamemakers would be put to death by the Capitol. So she and Peeta both take a handful of the poisonous berries and prepare to eat them in a dual suicide.