Because surely one of the most popular social media platforms in the world, operated by the enemy, with access to troves of personal user data that can be used for election interference, blackmail, propaganda, etc. is a national security threat.

And yes, other social media platforms, including Facebook, pose national security threats as well, but it’s up to the elected officials to decide how significant the threat is, and when/if it’s necessary to take action. With regard to TikTok and WeChat, I’d say it’s long overdue, and I personally hope the list will be expanded to include all software and hardware operated by Chinese companies.