Kings, or their advisors, referred to as a court, when not directly writing about a subject themselves, were the only ones who could designate, approve, and sanction writers as acceptable authorities[2].
Subject matter can vary in terms of plot, but the didactic point of the work is almost always to illustrate what authorities would consider the proper comportment of individuals within the authoritarian society.
Since most people don't enjoy the feeling of being written down to, the more successful (or popular) authors of such literature were the ones who best disguised their didactic purpose, or employed various forms of misdirection.
While didacticism forms a significant component of Shaw's, Orwell's and C. S. Lewis' fiction as well, their works can not strictly be considered as authoritarian literature because they were not writing at the whim of political leaders.
Practitioners of this genre in the aforementioned countries are routinely subjected to harsh sanctions, and many choose to go into exile in order to write freely.