The 3 and 4 night itineraries out of PC are their cash cow. They can charge more per night than longer cruises and they pull in many guests of WDW who are new to cruising. Being close to WDW is the key there. There will always be a ship positioned there and since it's the new ships that get all the press/media attention, people who never thought of a
Disney cruise will then start looking at them.
Those of us who have cruised
DCL multiple times already are mostly the ones looking at the new itineraries, wanting more variety.
We still book 3 or 4 nt cruises to the Bahamas, and will be sailing a 4-night on the Dream on Monday if my niece recovers from covid in time to care for my dad while we're gone. This will be DCL cruise #26. Sometimes you just want to relax onboard and don't really care if it even leaves the dock. The Monday-Friday itinerary works well for me because my niece stays with my dad M-F and I take care of him on the weekends. My situation is unusal and it won't last forever.