Maybe not by 90% but by a significant amount. Just doing a quick google for the userbase of TT by country and the US is the largest market with ~113M users [1]. What would happen to any company if their largest userbase just vanished overnight?
Then why are they serving 93% of their customers, especially when there is low overlap between those users? 90% of the american feed was american tiktoks.
[1]: https://worldpopulationreview.com/country-rankings/tiktok-us...