This is just a guess, I have no factual proof, but is it possible it is purely for aesthetic or decorative purposes?
I am guessing in cruises, hotels and other festive, leisure, touristic or vacation occasions meals often have a certain flair, and presentation is a big part of it. Plates, tables, rooms, etc. are often adorned with purely aesthetic artifacts like small sculptures or ornaments made of fruits, vegetables, other edible and non-edible decorations.
I imagine larger pieces (of any material) provide more creative freedom. By yielding larger chunks, bigger vegetables be cut into different shapes and allow sculpting more inventive forms with attractive appearances.
Carrots for their consistency and bright color make a good edible medium for these decorations, and larger ones probably provide the artist/cook more freedom, less waste and flashier results.
Alternatively, maybe some particular dish served on board also requires larger carrots, like some sort of stuffed carrots, or something served over a carrot as a vessel.
There may also be economic or logistic reasons, like saving space and money. Ships generally have inherently limited storage space; larger products pack better and store more efficiently by wasting less space per effective amount of usable product both saving space and money aboard a cruise liner.