Proximity and ease of access to information about them. They try to tell the same stories about China, but know they can't be too outrageous, as a lot of people in the west can visit China, or have friends and family there. Same with Cuba. They have to stick to vague accusations of "authoritarianism" in their propaganda, because people can visit quite easily and easily prove the west's claims wrong.

Very few people in the west actually visit the DPRK. This means the west can claim practically anything about them and have people believe it, because they'll never meet anyone who will go and check. This is quite different from the propaganda they get in South Korea, where it emphasises how poor and struggling the north is, rather than making up claims about Kim Jong Un riding an invisible unicorn to work or whatever. The south is much closer, speaks the same language, and a lot of people in the south have family members across the border, so making up claims that insult the reader's intelligence like in the west wouldn't go over well. But in turn, it's also illegal to say anything positive about the north in South Korea, it gets you jail time. So they have to be much more direct in their censorship of reality because of that close proximity that the west doesn't have. (It's also a bit of a cultural thing I think. Westerners are so fiction brained that they want a cartoonish villain who does things like in a movie, because they consume more fictional media than media actually focused on reality).