I think it's easy to say the ban doesn't make sense when it is perhaps a preventative measure. We have seen social networks take over others many times in terms of popularity. If TikTok and WeChat's usage becomes more widespread in the voting population of the US, they would have a lot of influence by controlling what kind of content its users sees; e.g., FB has been criticized many times for this, namely performing…
It is documented fact that FB, Google and the rest are tapped by US intelligence agencies. Anyone remembers Snowden? We know for fact that pretty much every single global US network works with the US government, but when comes to TikTok and WeChat something yet to be proven(I am sure they do but the evidence is weaker than the evidence if US internet companies working with the US government on surveillance). https://en.wikipedia.org/wiki/PRISM_(surveillance_program)
EU was trying to fix this through GDPR and such but US seems to desperately wanting to embrace the Chinese model and with US cultural lead, this will inevitably open the way to other governments ban FB, Google and the others because if TikTok is a national security risk to the USA then obviously Facebook and Google are to them. Probably Amazon and all other ad networks too. Anything that can be started from a dorm room will no longer be able to go global.
This will lead to a world where if you want to do a global project you will have to incorporate in every country you want to operate. It is even possible that internet to break up in patches and operating even a forum website becomes like Coca-Cola opening a plant in another country.
It is a very bleak future for humanity if you ask me. Can be good for local businesses though.
I wish the US went the EU path(regulating data handling) instead of Russa/China path(banning) so we could still have global networks and kids in their dorms could continue creating products with global impact.
What a shame.