If I check into a hotel, and the entire hotel is unexpectedly locked down (i.e. government forces are preventing anyone from leaving) due to an unrelated guest having Covid, chances are I am not paying - you simply walk out of the hotel after the quarantine is finished. If they want to find you and bill you, they can attempt to do so

If you are flying into a country where you have to self quarantine, ideally immigration authorities will inform you of that requirement, and you will likely have to pay for lodging/ If you cannot afford to pay for lodging to self quarantine yourself, you either have to be transported to a hospital or some other kind of public accommodation or put back on a plane to your original country of origin.

This is why international travel at this moment is kind of risky - too many unanticipated costs that may be imposed on the traveler