The USA is also willing to defend Taiwan and currently the US has carrier groups in the south China sea. This suggests that the idea of building chips in the US may be a diplomatic courtesy and arguably an incentive.
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Personally, I think we're at the point where the US would consider the costs of Taiwan's defense well beyond any potential benefits. It's too economically integrated with China, and the sheer number of bodies it would take aren't worth the moral victory.
Hong Kong is the writing on the wall. China wishes to restore integrity to what it regards as its territory.
TSMC must open facilities in the west because its Taiwan facilities are too dangerous to leave in enemy hands. It has to invest in capital outside of any potential conflict zone if it plans to exists over the long-term as a profit-making entity.
It's only a matter of cost: training an american to do the job of a chinese for the same cost is impossible today because american would refuse to produce these under the same condition: they prefer to enjoy using the chips rather than making them.
The good news is that the chinese will eventually come around and start changing their expectation.
If you think China cant change, look at their drastic demographic changes: they can become what we became, they just take longer.