that said, banning their operations appears to remove any legal leverage the govt might have with the company while still dealing with the app being installed everywhere, which seems clumsy. with less than a year left in office the govt probably doesn't have any remaining runway for strategy, so this may just be posturing. there are a lot of ways to look at it.
cynically I might speculate there could be a domestic surveillance/interception rationale for making them close their operations, as the app is a full communications platform and if it backhauls to a domestic regional data centre, the federal agencies need warrants to do interception and would have to give their monitoring tech to the chinese company on their premises, whereas if the traffic is international, they can do mass interception using their existing mandates.