It wasn't until I used TikTok that I understood why it's so scary. Just based on how you interact with the app: how long you watch, what you like, how fast you're scrolling, etc. it starts to show you videos that are eerily related to what's going on in your life and what you're thinking. You don't even have to search for topics. You just start getting videos that seem to be reading your mind. The idea that they can tell what huge swathes of the population are thinking and feeling is scary. I think that's got to be a huge reason they want it under their control: it's sort of a mind-reading app.