A massive, comprehensive data privacy law would've covered the TikTok base and any software by any other threat

That's assuming the ban is motivated by privacy reasons, but i don't think it is. It's far more likely that it's because the US has no control over the platform's algorithm, which they fear is feeding Americans media and perspectives that are antithetical to their foreign policy objectives (Blinken and Romney have both stated as much).

A US buyer would be more friendly/responsive to US regulatory influence. That's the only reason this isn't a privacy bill instead of a ban or forced sale.