Good point: there should be interest.

Just like the interest you earn on your health insurance?

You actually do earn interest on HSAs right? I don't know much about them other than the bit I read, but they seem to be all the rage nowadays.

Yes, but an HSA is explicitly not an insurance account; it's a tax-advantaged savings account you use to cover routine, predictable medical expenses while a high-deductable insurance plan covers broken bones and gigantism.

Insurance companies invest premium payments, mostly in fixed income, so one would expect the current interest rate to be a factor in the cost.