I am sure that the price increase was a shock, but the company does not owe anyone an official communication on the justification.
They raised prices because it increases their revenue and they believe people will pay it. That is what businesses do. If no one buys beer or soda or if people stop cruising Carnival because of it, they will lower them.
Did they increase the price of Cheers and Bottomless bubbles? If not, that might be the way to go. I am cruising in Australia in a few months myself. Yes, a price increase on beer and soda is disappointing to me, but I won't let it ruin my trip.