I agree with you. But cruise lines are not "American companies". Most of their customers are not even Americans.
Whatever caused an "oversold" situation, be it a booking system issue (unlikely), cancellation of another cruise and shifting the customers to this cruise, greed (let's sell the same cabin for more money), etc, should have serious consequences for cruise lines, by law.
Already this costs Celebrity $450 per person, $500 per person for flights, many customers who chose to cancel and get a 100% refund (loss of sales), customers who will not book again with Celebrity, agents busy dealing with this instead of selling more cruises, etc.
My strong impression is that this whole fiasco is due to bad management, lack of planning and bad decision making. Even without this incident, I think the cruise industry made a lot of management mistakes that annoyed customers and hurt sales.
I own stocks in RCL.
We need something (regulations) that will force cruise lines to save themselves and be better managed. I doubt that will happen. I think the trend is worse and worse management + worse service for the cruisers.