The reason that
DCL does not offer dinner in Cabanas is staffing. Each ship has 4 dining crews - MDRs plus Palo/Remy. If all the MDRs and Palo/Remy are open, there is not enough dining staff available to work in Cabanas.
Our past cruise, Cabanas was open for breakfast on debarkation day - this is the first time, for me, that I have seen this. What was more interesting, it was the cooks and staff from Remy/Palo that were working Cabana's - some of the MDR staff found this humorous
But, if the MDR staff did not have any of their guest eating debarkation breakfast in the MDR, they were sent up to Cabana's to help the Remy/Palo staff.