I think the difference is that in China the public are aware of the policies and they know how it will affect them if they say something dangerous. This keeps the power in check in a way since they can mostly only act on policies they have made clear before. In the US there is a false sense of freedom which makes the reasoning of power opaque and unchecked.

"None are more hopelessly enslaved than those who falsely believe they are free." – Johann Wolfgang von Goethe

This joke worked for previous presidents. You can't do it any more.

Also it's never been true you could just approach the American president or the Chinese one