It's the length of the cruise, the high number of sea days, the passing of the Panama Canal and the moderate cost per night (for
DCL standards, that is).
Also there is a low number of guests: mostly all staterooms will be occupied but a much lower number of people per stateroom. Combined with the length of the cruise this gives a lot of relaxation on activities.
Due to the length of the cruise and the timing out of school holidays there is a very low number of children onboard (around 300 vs 900 on a school holiday cruise), which gives these few children a lot of attention from the youth councilors and gives the adults a lot of space on the ship and even adult-exclusive activities in the kids-clubs!
As the regular entertainment schedule runs out after a week a lot of additional activities are organized that are not on the shorter cruises. The most hilarious of these was the Officers hide-and-seek !!
Most activities are a lot more available: 14 days available in the Spa, so no rush on pre-booking, Palo Brunch was easy very easy to get, especially in the first week, we had 3 brunches and a diner. Only the Panama Canal crossing day will fill up quickly with brunch.
Ports are not the main attraction of this cruise. We were on this year's WBPC and from all ports we liked San Diego best, but to get from Miami to San Diego a plane would have been quicker and cheaper. So if you cruise to see a lot of ports and don't bother about sea days this cruise is definitely not for you.