Most wouldn't book the quarantine so there has to be a rule requiring proof.
Wow I suppose someone must be paying you to say this.
Ok to your point, if someone doesnt book the hotel they can be fined at the airport and then escorted to the hotel. If I can prove my due deligence in trying to call the line with the best of my efforts, I will be awarded justice. If not I will pay the fine and pay for the hotel as well.
This is such a nightmare situation that keyboard warriors would never understand.