Imaging you were hosting a dinner party(not a potluck)and your friends brought and ate their own food, how would you feel? If U.S. athletes ship their own meat to China for the Olympic Games, it will be like a slap in the face of the host, China. From BBC News :
China has expressed regret that the US has decided not to trust its food during this summer’s Olympic Games.
The US delegation has said it is planning to bring its own food for American athletes.
At a news conference in Beijing, a senior official, Kang Yi, said it was a pity that the US had apparently decided not to trust China’s food.
See also the Washington Post article: China Defends Olympics Food Safety