My bet is that TSMC recognizes they are a crazy geopolitical pawn. And is frankly playing their part.
Once China develops chip production abilities similar (but not necessarily better) to TSMC, they’re free to destroy Taiwan. Then they’ll be the sole cutting-edge producer, meaning that everyone will continue to do business with them despite their behavior.
TSMC and the US recognize this. If TSMC bring their tech to America, they’ll at least be safe to continue manufacturing (“for the shareholders”). It also is self-serving because it changes the geopolitical game. It increases the risks to China of an invasion, and favors to the US increase the odds of US intervention (good for their patriotism).
Finally, it’s pretty well established that the US defense industry prefers local factories for security purposes. They’re obviously interested in preserving this ability domestically, and most companies recognize that and accommodate.