I agree with Marty,
There is even more involved to pull a ship out of service. Many cruisers have planned for a long time for the cruise, have scheduled vacations that may not be able to be rescheduled and made other plans that would be difficult to "unmake". (Another good reason to buy trip insurance.) But after the initial disappointment of not being able to go to the scheduled ports, I would rather cruise than not.
A change in itinerary is particularly disappointing to first-timers but I encourage a chin up approach. We haven't cruised so much that we don't look carefully over itineraries when we do our planning. But now I take the approach that a missed port gives us another reason to book that next cruise.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014
Star Clippers: Royal Clipper 2015