It's certainly easier to enforce laws and observe manufacturing processes at domestic factories than it is at factories thousands of miles away in a country that actively encourages IP theft and other wrongdoings, don't you think?
Now imagine how much it'll cost to stay in lockstep when the level of sophistication becomes "a single component the size of half a grain of rice".
If the question is "why don't we move chip production to the US, so this doesn't happen" the answer is "because you might be able to do that for one or two plants. And it'll probably drive up the price by an order of magnitutde, so they'll go out of business soon after. And you sure as hell can't move the entire industry because of prohibitive cost and shortage of manpower to do the bit that you want tacked on that can't be trusted to be done abroad".
The moment the option of taking control of a production line of something _this important_ becomes available, your local specialized organized crime outfits will start to figure out ways to insert themselves into those production lines, learning the ins and outs, and figuring out a way to get something, anything, in there that won't be noticed but will give them a hook into millions of systems.
The law does not prevent crime. It just puts a price on it. While that price is typically too high for individuals, for organizations that have no business registration to revoke, and no CEO to drag to court, it is an entirely trivial cost.