It is the massive subsidy (bribe) the US people are paying TSMC to build the plant in the US, agreed under the Biden Administration.
“Under this agreement, TSMC is to receive up to US$6.6 billion in direct funding from the US government and could get up to another US$5 billion in the form of loans.”
It is government intervention in the free market that will likely lead to oversupply in a few years.
https://www.taipeitimes.com/News/biz/archives/2024/04/09/2003816137