In layman's terms, it's simply a "Big Fat Lie". Some would call it "marketing". Since there are no "down votes" that restrain countries when it comes to naming themselves, they can choose not to call themselves the "Oppressive Hell Hole that You Really Don't Want to Visit", and instead choose something like "Unicorn Land". In politics, country names are not the most offensive lies being told.
Edit: Other examples to ponder: Greenland and Iceland. Not exactly examples of "truth in advertising". But just like North Korea, people worldwide know what's to be found in each of those places. While some country/territory names may be a bit ironic, they are still preferable to "Location 317" and "Location 1462".