You can also do this in the DPRK.
Maybe. But Cuba doesn't stick tourists with guards through their entire trip. That's a pretty substantial difference.
Also I'm curious as to why they do that. I always assumed it was for reasons of national security. It seems perfectly believable that the DPRK is under a substantially greater threat of imperialism than Cuba, after all, and people tend to forget that. The US doesn't regularly do joint military exercises with local hostile nations just outside of Cuba.
I'm not necessarily trying to criticize the North for their policies towards foreigners. By all accounts that I've read their officials are very cordial and considerate, if rather strict and conservative. But also by all accounts, they are by far the most closed and secretive of socialist countries. It's hardly arguable that they are as open as Cuba. Again, I don't intend it as criticism. It's not my country, and I have no platform on which to correct them.
Because it's an entirely different culture? (Unlike Cuba.) Because nobody knows anything about what's really going on inside the country? (Unlike Cuba.)
This. Cuba's Spanish heritage gives it's culture a lot of European characteristics. I expect that their culture will not be that starkly different from my own. Korea, however, is a different animal altogether, it's about as far from the west as you can get, and by every indication the DPRK has been extremely diligent to make sure their culture is distinctly Korean with as little foreign influence as possible.
When I go to North Korea, I'll probably be with a KFA group. Though I can't help but be concerned with some of the things I've heard about them. They're supposedly very intolerant of under-zealousness.