[bsder]

1) Because Apple never had any volumes even remotely large enough to move the needle.

The Commodore 64 moved way more units than anything Apple ever did until the iPod and the PC dwarfed even the stuff Commodore did. Apple doesn't even move a half-million laptops in a year today. Everybody caters to Apple's low-volume stuff solely in the hope of getting access to the iPhone volumes.

China's current "supply chain expertise" is a result of massive, long-term support from the Chinese government. And I say that with envy! There is nothing in particular stopping that from being formed here in the US other than that long-term support. We have all the pieces, but nobody is going to take the risk to expand significantly beyond their current demand without guarantees from the government (and that's just smart business).

2) Because nobody in the US wants to manufacture

Everybody in the US wants to be "fabless" because that optimizes profit. The problem is that somebody has to do actual manufacturing, at some point. As we found out with Covid, "fabless" translates to "last in the queue" when things go wrong.

Nobody in the US wants to do the capital outlay and risk to do physical manufacturing. See: the current grief with Intel or the Chinese-owned steel mills in the UK. By contrast, if those were Chinese companies, the Chinese government would be pouring money into them as they would regard them as a strategic asset.