You never know what could have happened. Maybe there was a tragedy. Maybe they all quit because of something management did. Maybe they all had the flu. Whatever it was, it happened and although it was disappointing and a waste of a trip,stuff happens.
When you complain you are looking for a remedy, but I am sure they are already on it due to the fact they had to close and lose revenue, so this seems like complaining for the sake of complaining. Not sure what it will accomplish.
They could have given discounts to customers showing up to apologize but I guess they had other things going on.