There's nothing preventing China from buying mass data from Facebook or one of the many data brokers. This is about censorship and the ability to control public narratives.
Yes there is. Facebook has never done anything like this and never would, that's what is preventing it.
You're falsely equating mass data. If anyone can buy the data from brokers then it's effectively public and could be weaponized by anyone. If TikTok collects their own data and doesn't sell it, then it's not public and can be weaponized exclusively by the Chinese government. And that's separate even from algorithm manipulation, which is another liability that's difficult to catch & prove definitively.