The US regulators and government is not tired of collecting money from and imposing fines on all social media and tech platforms, hence why Facebook, Google (YouTube), Instagram, Snap, etc all have been fined by the FTC for privacy violations.

Facebook and TikTok are of similar sizes and have both violated the privacy of its users and since FB has paid a giant billion dollar fine to the FTC, it already makes sense to also fine TikTok on similar grounds including overseas access to US data by specifically targeting US journalists.