While I think some of it is the UX, the main thing in TikTok's favour is the massive number of people creating concise, interesting content for it.

YouTube videos are frequently 30-120 seconds of relevant content padded to 10-15 minutes. Most TikTok videos are close to just those 30-120 relevant seconds.

If Congress bans it, they'll probably lose the trust and interest of a massive percentage of Americans under the age of 30.