OP, your posts perplex me.
It's irrelevant as to why China does anything. They are a restrictive state, where individual choice, be it a child or an adult, is massively limited.
Whereas in Western countries, the choice about how social media is consumed is left with the parents, in China, and similarly-governed countries, it's imposed by Government.
It's not about 'what they know'.
I have three teens (or nearly). Like all parents of teens, I'm constantly fighting a battle around screen use / time. However, I see positive benefits to social media, in terms of community building & socialisation, as well as a source of knowledge. I work at third level & social media (as part of our engagement) is a key point of engagement with our students and is enormously beneficial.
Of course there are dangers & downsides.
These are mitigated by limits & boundaries, as many naturally imposed as possible eg they all play sports which takes up a lot of time, evenings, weekends etc, and it's a completely different environment to online. So I'm fine with them then engaging online, scrolling, or making content (like TikTok videos).
There's great stuff on TT. You are being utterly alarmist. My eldest DD is aiming to study medicine. She follows other students on both TT & IG who share their experiences of studying for / applying for medicine.
Finally, as with so much, it's also about conversation. I ask my teens not to go on their phones when we're in the car, so we talk, no screens at the dinner table, and they often show me content on TT, and it's enjoyable & a way to connect.
The principles around teen well-being have not really changed over many decades, despite the advent of technology.