I believe there are fewer ships doing the western itinerary during the summer these days, but they are larger. Although fewer ships stop at Ocho Rios, they are all very large - pretty much the equivalent of twice the number of ships from a few years ago from a passenger loading perspective. Looking at the port schedule for Ocho in September, there are 11 ships calling, with the smallest being the Carnival Destiny at 3360 passengers, and the largest are both Freedom class RCI ships at 4375. This all adds up to 43,000 possible cruise passengers for the month, or the same as 20 or so 2000 passenger ships.
But enough statistics. Other ports have developed more, while Ocho has been stagnant as far as things to do for a while. Having ports close to each other, such as Cozumel, Costa Maya, and Belize, means more fuel efficiency for the ship. And the major sticking point for a lot of repeat cruisers is we are weary of the hassles one encounters in Jamaica.
I also looked at the fall schedules and 16 ships stop there in October and November - which reflects Princess returning to the Caribbean for the winter and spring.