Everything that NK does is in order to keep those people at the top. It is the absolute definition of a dictatorship. Kim Jong-un only wants to maintain his own wealth and control. That is the only goal
It's too simple view to be true. For one thing, Kim Jong-un understands that if he's not in control, he and his family members are dead. Of course, they want to maintain wealth and control, just like everyone else. But they also don't want to become dead. And they're dead in either of situations:
- if they relax the control
- if some other country decide to "liberate" NK
They probably don't see any possible way out.