But they cannot buy the same data - the quantity and quality of the data they obtain themselves (through apps like TikTok and WeChat that are running in the background 24/7 while collecting any information possible, such as secretly copying your clipboard which is likely to reveal passwords and other sensitive information) is far higher than what they could pay for.

You’re also ignoring the fact that they can use their apps to easily spread propaganda and influence elections. They’ve already censored videos that criticized the Chinese government. And inside the app then they have a very prominent “Covid-19” button where they can cherrypick what information to display.. they’ve for instance chosen to omit the fact that the Wuhan Virus originated in China.