Well, I don't pretend to be a cruise line CEO but even I can figure out that its less expensive to buy blocks of seats on commercial carriers than run your on airline.
Even if you bough a bankrupt airline you probably couldn't be profitable against the big boys.
What they could do though is pay the baggage fees and wrap the transport into the package and provide an "all inclusive" air transfer service. Once you put your bag on the airplane you don't have to worry about it again until they deliver it to your stateroom.. I'd pay a bit more for having all of that arranged for me.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007