Good discussion to be had here, but to be that guy plenty of other non-monarchist states like the US have multiple leaders from the same families (Bushes, Roosevelts), the tendency of power to concentrate with prominent people and thus their families which leads to political dynasties is a pretty universal trend

Yes it's a trend that should be opposed by Communists in the long term, but I don't think having 3 successive leaders from one family is necessarily an indictment of the DPRK being that it is a relatively young state that has been at war with the world's largest military power since basically it's inception

This article titled, "Is North Korea a monarchy?" might help clear some questions behind this. I will add the following excerpt that might contain the answer that you are looking for:

But there is one clear pattern – the leaders are from the same direct bloodline. Now explaining this is where nuance and context are vital and, uncoincidentally, where Western media often abandons all such nuance and context. The Juche Idea created by Kim Il-Sung as the ideology of the WPK, and later DPRK, says that “man is master of the revolution”, however, only with proper leadership can the creative potential of the masses be directed properly towards the revolutionary goal. [6] This shows why leaders almost appear larger than life because in modern Korean culture they are respected as having much more significance to the state of things than they do in the West. Perhaps this is also influenced by the fact that the DPRK’s government acts revolutionarily, whereas in the UK at least, our government acts in a reactionary manner.

This idea likely originated from the fact that in Korea, the ‘leader’ is seen as very important and respected figure. This rationale can be traced back to the philosopher Confucius, who is the pillar of most East Asian nations, or at least he used to be in recent history. By this I mean, as liberal philosophy dominates the West, Confucian philosophy dominates the way of thinking in the Far East. Confucius himself wrote on leaders and how they should be honourable and always humble if they are to earn the deference of the people. This went on to be the model for leaders in the East and the people came to revere the position more (depending on the success of its application) than what happens here in the West.

For more context on the history of the Kim family, Kim Sung-Joo, later named Kim Il-Sung, was a revolutionary and a national hero, who led the Korean people against the Japanese and American imperialists and won himself masses of support from the entirety of the Korean people. He guided the ship of state, at the will of the people, until he died in 1994. [3]

He had a son named Kim Jong-Il who had, for many years prior, been embarking on a political career in his own right and had won positions across government for his dedication and impressive competence for leadership. He only came to power four years after the death of his father, who he never publicly referred to as such and always called him “leader”. On top of all this Kim Jong-Il came to power in a time of great crisis in the DPRK as the socialist camp had collapsed and those few who remained were scrambling to survive. Furthermore, the North Koreans found themselves under a new economic offensive by the American imperialists in terms of new sanctions. This would have led people to observe the young Kim in the context of both his impressive credentials and in light of him being the son of the great leader as being the natural candidate to fend off this new assault. This is natural as in all democracies to people look to who they think of as the best leader and is irrespective of the parental connection between the two. It would be a lie however to deny any correlation.

Finally comes Kim Jong-Un who built himself an impressive portfolio of roles and like Kim Jong-Il (his father) he did not come to power immediately after his death. This was because their constitution does not allow for a monarchy, and instead, it places power in the hands of the Korean people to decide.

After all of this, I would argue that it is clear that the DPRK is not a monarchy and only a dictatorship in one sense – it is a Dictatorship of the Proletariat.

Kim Il Sung is still extremely beloved within the DPRK and seen as a national hero so that probably had an influence on the population’s opinion of Jong Il and Jong Un too. Plenty of countries see this; in the US, Prescott Bush was an extremely influential politician, and then a few decades later his son and grandson became presidents and another of his grandsons is governor of Florida. Both Jong Il and Jong Un already had political influence and careers within the country before they became leader.

An interesting take:

A dictatorship of the proletariat can be a democracy (in the purely formal sense of "democratism"), it can be a republic, it can even be *aristocratic" or monarchical. After all, why not? Saudi Arabia is no less a bourgeois dictatorship (in its political form) just because it re-presents itself as a monarchy (in its institutions).

A monarch may be a functionary of the proletarian class in just the same way that they may be a functionary of the bourgeois class--whether not such an institutionally monarchical proletarian dictatorship is at all desirable is a separate question.

The origins of proletarian dictatorship, in the underlying polity, are not "statist" (in the sense of state institutions), but political--i.e. in the polarization of the polity according to the privileged subjectivity of a certain class for class coalition).

Formulating the concept of the proletarian dictatorship exclusively in terms of a "state" is an error. It is something prior to state institutions, something which expresses itself in state institutions. This dictatorship is not identified with the state, but is the generic form of a state ruled by a certain class within the context of a certain polity.

The modern dictatorship's power of dictation issues, first and foremost, not from the state, but from the triumphant class and the seat of its concrete power in the industrial and agricultural base, that is, it issues from the grounding of a political form in the polity. The state, as the institutional expression of this concrete power, arises as a re-presentation of the latter.

This concrete seat of power is the underlying whole which is constitutive of the polity, and the proletarian dictatorship is the generic form of the proletarian institutions that reflect this polity, a generic form that specifies itself in particular institutional arrangements that are, in turn, bound to express themselves in a diversity of forms contingent on historical conditions, national peculiarities, cultural inheritances, as well as explicit theoretical considerations.

https://chateauschmatte.substack.com/p/class-dictatorship-and-sovereign

(I am still learning but I would consider DPRK/North Korea still a dictatorship against capital. I would be interested in other MLs' takes on the above analysis.)