Because simply US is dealing with different types of threats than China/Russia do. Priority for US is the terrorists. I don't know about Russia but the priority for China is the anti-government folks. Terrorists never speak out so you never know who they are. So everyone is assumed to be possible terrorists by the US. Thus everyone gets harassed. But the anti-gov folks have to speak out, everyone knows who they are. It's way easier to pick them. Chinese border control is not interested in your illegal electronic docs at all as it is impossible for you to disseminate them in China and if you were caught on that, it is a totally different agency to come and deal with you. And I guarantee you don't want that.