They may be relying on the on board spending to make up the difference?
Most certainly they are. Drinks, extras, tips (gratuities,) tours, shops, hairdresser, beauty parlour, photographs, casino, etc, etc all are
never discounted. And let's face it eight non stop days at sea is really intensely boring, so what else is there to do but spend?
Cruise ships rely on the client to spend more than the fare whilst on board. Is it still in dollars?
I wonder if Carnival / Cunard are finding it rather harder to get 'bums on seats' in three Cunard ships?