the DPRK has the benefit of having a land border with a friendly power, whereas Cuba is 13.5k km from the PRC by ship which is a far harder transport method to ignore embargoes with
on top of that, Cuba needs oil for power and are a net importer even with their relatively low consumption
they do have oil deposits, but it is of a difficult to refine kind of oil, requiring advanced machinery that would need to be imported
all of this on top of being an island in the middle of a heavy hurricane zone
Cuba has it very rough