Free trade generally does not mean you have to let foreign companies operating in your country do things that domestic companies are not allowed to do.
Most of those sites are not in China not because China says that they cannot operate there but rather because China say they would have to obey the same rules Chines companies do. That generally involves things like storing data on Chinese citizens only on servers in China, censoring things the government wants censored, and giving the government easy access to information including identifying information to unmask anonymous posters.
This is post hoc nonsense. China blocked US tech companies so that they could copy what the US companies do without any threat of superior competition.
The point is that they get to access the Western market with their dancing video app, but Westerners aren't allowed to access their market with the apps they make. That gives those Chinese companies an unfair advantage in potential market reach.
A simplistic economic model that overlooks hundreds of important factors may provide a basic Econ 101 understanding but it does not reflect how the world truly operates and proves nothing.
Sure it's a simple model. But the burden of proof lies with the person claiming that free trade needs to be bilateral. That's not some inherent property of it, or something immediately obvious. A basic look at it past "It's not faaiiiiiir" actually shows quite the opposite
It's ridiculous to let Chinese apps and websites operate in the West when China blocks so many Western sites and apps: https://en.m.wikipedia.org/wiki/List_of_websites_blocked_in_...