it was the simple theft of those resources by the supporters and enforcers of the regime. This process didn’t just enrich the regime itself, it created an elite class of mid-level officials, bureaucrats, managers, and military officers who very much enjoy the spoils of wealth, property, and inequality, while continuing to advocate for socialist revolution. (I hope this is starting to sound familiar.)
It's not-? The proliferation of middle managers and leeches on the system is rampant under capitalism too, and corruption erodes all systems; it's not like capitalism is so great that it's somehow immune to spoil due to corruption. And the "advocating for a socialist revolution" by North Korean bureaucrats is just, as you've outlined yourself, not sincere, so this isn't a rebuke of socialism but rather totalitarianism, which can lie with impenetrable impunity. Whether or not socialism is a workable system is not what's being tested in NK since that's demonstrably not the system they have, though they may call it by that name.

