In the past few years, many storms have forced countless changes for the ships which in turn have angered many passengers (why I'm not sure as you know it is hurricane season and who wants to sail into a hurricane?). That time of year is perfect for trips to Europe and Alaska, so why not move the ships to "better" places for those months?
Welcome to cruise-chat.
I take issue with your use of "countless" changes for ships during hurricane season. It really hasn't been that bad.
The simple fact is there are markets for all itineraries and abandoning the Caribbean under a perceived threat of hurricanes is simply not practical. Ships are not sailed into hurricanes.
And finally, Europe and Alaska have limits as to the number of ships they can handle. Alaska is already saturated.
You can't move every cruise ship to "better" places. Besides, many of us like the Caribbean in the summer.