They are all communist tyrants. Establish a totalitarian society and implement terrorist rule. Why is Kim Il Sung hereditary? But the descendants of Stalin have to flee the United States or stay in the Soviet Union but end up miserable?
Whilst there's always more to be said and more directly to your question this answer by /u/hedgehogsinhats may be helpful.
It's an older answer and thus might not be up to todays standards.