Soon enough, Chinese people would no longer be content with Chinese-made goods and services from small Chinese suppliers (e.g. through decentralized marketplaces like Alibaba) - Instead they would start buying US goods through centralized marketplaces like Amazon and Apple store - Basically the money would leave China and they would all be worse off on average.

By keeping western media out, they keep Chinese money in. Don't ignore the fact that media is paid for almost entirely by advertising and that advertising is paid for entirely by companies who need to sell products.

Both totally available in China already via their local forms (store.apple.cn and amazon.cn). My wife orders from Amazon a lot.

Economics aside though, there are enormously dangerous consequences to controlling the exchange of information.

Seeing China's nouveau riche and the general demand for western luxury goods, and hell even Buicks, you don't know what you're talking about.

What "US good" - all that stuff is made in China to begin with! Well, OK, not literally everything, but as interconnected as the global economy is, what you are proposing strikes me as pretty much nonsensical. China won't benefit from "protecting" itself from trading with the West.