Yeah there are lots of reasons. Tiktok has been proven to be harvesting browsing habits, biometrics (facial ID and fingerprints), voice identification, key logging, and more.
You are giving your face, fingerprints, and voice to a state sponsored entity in the age of deep fakes and broad sweeping intelligence operations.
If you’re pro China, then this is a good thing. If you care about identity theft, deep fakes, or your credentials being sold on the dark web, then tiktok is a Very Bad Thing.