CC
It is the health insurance companies who are receiving the subsidies. The money goes straight from the US Treasury to the health care company.
The person supposedly receiving the subsidy would not be buying the health insurance otherwise because they could not afford it.
I don’t see how a claim will stand that they are “underpaying their health insurance costs”. Yes, in practice they are, but they are being forced and coerced to do so. If they had that amount of money being given to the insurance companies in their name they might have decided to do something else with that money.
I think it’s important to be clear about who is receiving the subsidies here. It is the insurance companies.