I think because the DPRK occupies a more important strategic location re: Russia and China, it has invited a much more hard line stance from liberals than Cuba has. This is also part of the reason why China intervened in the Korean War and prevented an American victory in the first place - they didn't want the US right on their border.
Comparatively, Cuba is essentially just a culture war as far as the US government is concerned. It doesn't occupy a strategic position, it doesn't have large amounts of strategic resources, and the one thing that the US really wants from it - a naval base - it gets to have whether the Cuban government likes it or not. So the international movement that has risen in support of it has gone uncontested by America, and the island itself very nearly got its relations normalized at the whim of a single president.