National security reasons
the cop out for anything
in reality while there may be some concerns for national security, i very much doubt that there is a single bit of technology that could come from china that any other super economy could not prevent from transmitting data to anywhere they didn't want it to.
What congress is worried about is that their wallets might get a bit lighter if a cheaper chinese product came along and took the only thing other than weapons the US has of making money, technology.
Tiktok has already encapsulated the next generation, Huawei was eating away at Apples market share when they got banned and if China decides to Annex Taiwan, the US have no way to recover their technology sector until its new fabs are set up.
Make no mistake, this is about money with the cover of "national security"
