I was on a Royal Caribbean ship a couple weeks ago (Utopia, 18 decks, 5,668 passengers). It has 24 main elevators split between front and back, left and right. So a bank of 6 in front of you each time you needed a lift. You press your floor on a touchpad and it assigns you an elevator A through F.

I swear no matter if it was busy or not, it seemed like everyone was assigned to the same one or two elevators. The wait was always so long too, I used the stairs most of the time if just going <6 flights.

Someone besides RCCL needs to study that algorithm.

Possibly to balance the hours on elevator banks. Common in buildings to leave some out of the cycle, since elevator maintenance can be a year out to schedule. Probably much worse out at sea

This type of system is mentioned in the article under the "Destination Dispatch" section.