I feel the main reason is the fact that america is scared of TikTok popularity among its youth and the fact that the algorithm is being controlled by a company founded in China. Well, the fun fact is that Trump was the champion of the ban before during first tenure, and he wanted TikTok to be sold to an American company but now he is against the ban because TikTok help fueled is re-election and connection to the youth.

Well landed properties can be confiscated during war or conflict. So they don't really have potential harm to the host country.