While semiconductor fabs are highly automated, the machines are complex enough and do extreme enough things that they break a lot, requiring human intervention. MTBF for many of the machines used can be measured in hours, it's not like you can set up and go home. TSMC has around 65k employees overall - a cursory search did not yield their makeup by job breakdown, although from 1997 through 2003 around 50% of their employees were 'factory' workers via [0].

I'd expect high-margin items like semiconductors to be more amenable to onshoring anywhere - certainly Intel has almost all of its fabs in highly developed countries, but I think this is hardly a cost efficiency move - rather it's a hedge against the failure of globalization and the risk of the US losing access to advanced semiconductor technology in case of strife in Taiwan. Russia has already lost this access. TSMC took in about $56B in '21, of which about $28B was 'cost of revenue', the amount they needed to spend on supporting this revenue (marketing, legal, production, e.g., not building factories or R&D). There's certainly room for increased production costs while maintaining a profit.

[0] - https://www.researchgate.net/figure/TSMC-personnel-structure...