I think the reason is less about “i, an individual, am getting my data harvested” (though certainly still a factor) byt more because China is still very much considered an enemy of the US, and they are not only harvesting americans data in a very invasive way - as in, recording pretty much everything you do on your phone, not just in the app - but an adversarial government now has access to all of that. Additionally, because the chinese “free market” has been effectively neutered in recent years, high chance that the CCP is able to influence TikTok’s algorithm to affect what people see and push propaganda. People should be concerned about it in the same way people should be concerned about russian bot farm, but more so, because there isn’t an audience of millions feeding russian bot farms their personal information.