There's a chance that the real reason why they want to ban Chinese models is that they are so good at fixing bugs and preventing exploits that intelligence agencies have been using for espionage and surveillance for a long time.
I don't think this really works because the Chinese government is going to be incentivised to tip off the US companies to deny the US government those exploits. I guess maybe that's what the open source patch program here is about, making sure banning the models doesn't work because they can just report the exploits without the company running the model themselves.
How does banning the models in the US prevent this?
when in doubt, it's better to assume capitalism than anything else.
Anyone who knows anything realises banning things is a) impossible and b) your enemies will use them anyway, you are just depriving your own side of the advantages.