My read on the situation is that this is the beginning of clamping down on _all_ (or most) of this. Also important to note the difference between racism and national security. The notion isn't "wacky chinese people ooh so mysterious so sneky", it's that the government isn't the US's ally and has (valid) reasons to want to reduce the US's grip on the global stage.

It's not (just) that it poses an economic threat to one of the biggest US companies (which as you said, I'm sure plays a big part in why it's suddenly relevant), but that it allows a government-influenced foreign media channel to influence policy indirectly by means of mass dissemination.

As for why now and not before, it's because of how apparent the possible effects are now that there's a very direct and widely spread channel that can pump OUT information, which is vastly more effective and obvious than passive surveillance through cameras or other hardware. (Also cybersecurity people have been calling out this sort of stuff for hardware since time immemorial)