They could just not cover injuries where a seatbelt isn’t warn.
That said, we have evidence that seatbelt wearing didn’t impact insurance rates. Literally look at the rates over time, even after these laws were enacting, insurance rates rose fast as ever
That's not how emergency room care works. It doesn't matter whether it's covered or not, you're going to get treated; quite likely the hospital ends up eating the bill if insurance doesn't pay.
That said, we have evidence that seatbelt wearing didn’t impact insurance rates. Literally look at the rates over time, even after these laws were enacting, insurance rates rose fast as ever