>So they're not 'forced' to per se - but if they don't sell they'll lose a large part of their market. Or am I wrong?

Correct.

The US is 10% of TikTok's user base, but accounts for 50% of revenue. Further, most of TikTok's most popular users are American (https://en.wikipedia.org/wiki/List_of_most-followed_TikTok_a...).