It's important to remember that North Korea is strange even by communist standards. In the Korean War it could be said that the USSR, PRC, DPRK were more or less a united communist front. But this wasn't to last, and only three years later the PRC and USSR started bickering, eventually becoming feuding rivals after the Sino-Soviet split.
The collapse of communist unity led each communist state down a different path. After Mao's death the PRC under Deng Xiaoping decided upon economic reforms. Deng famously said that it does not matter what sort of cat it is, so long as it catches mice. They justified this ideologically as a return to Lenin's New Economic Plan, which Stalin (and thus Mao) had rejected, and the USSR continued to reject.
The PRC and SRV regarded economic reform as essential to political survival. The DPRK however became more and more of a bizarre caricature. While both the USSR and PRC reacted to Stalinist failures by veering away from their absolutist policies, the Kim regime went the other way. What had in the USSR and PRC been temporary policies became eternal features: the personality cult, the gulags, famines.
Economic reforms like Deng Xiaoping's are unthinkable in the context of dynastic Stalinism, as it would undermine the absolute authority the Kim dynasty has over the lives of North Korean people.
The emphasis of the USSR after Stalin, and the PRC after Mao, was on how socialism could improve people's lives. Which goes some way to explain why Richard Nixon and Nikita Khrushchev had passionate arguments about who made the best domestic appliances. The DPRK has never tried to compete on those terms, and like Stalinism and Maoism it is primarily concerned with military matters. Survival, not prosperity, has been the point of the regime, and the ideology has evolved to match this purpose.