I do not know the real answer, but my guess is this manufacturing was offshored like everything else because almost anywhere outside the US is cheaper. Mexicans, Indians, and almost any other impoverished people were too stupid to manufacture semiconductors. The Chinese are smart enough but their “don’t give a shit, push units out faster” attitude made them incapable of making semiconductors that worked (they can put chips on circuit boards though, still better than most). That only left Taiwan. Poor enough to be cheaper than the US. People smart enough to handle the job (mix of Chinese and Japanese). Not horribly corrupt and confused by the concept of quality like the Chinese.