In Children of Dune, a politically aware mentat, namely
! <PERSON> resurrected as a ghola
thinks about the galactic power structures. His thoughts:
Planetary feudalism remained in constant danger from a large technical class, but the effects of the Butlerian Jihad continued as a damper on technological excesses. Ixians, Tleilaxu, and a few scattered outer planets were the only possible threat in this regard, and they were planet-vulnerable to the combined wrath of the rest of the Imperium. The Butlerian Jihad would not be undone. Mechanized warfare required a large technical class. The Atreides Imperium had channeled this force into other pursuits. No large technical class existed unwatched. And the Empire remained safely feudalist, naturally, since that was the best social form for spreading over widely dispersed wild frontiers - new planets.
This is about the stable state of the current system, rather than how it came about, but that's still relevant. Let us expand on this a bit.
1. Space travel is expensive and difficult. Only the Guild maintains the ability for interstellar travel, and it exists in a state of tension with other centres of power. Therefore, individual planetary systems are isolated from one another. There are large-scale institutions such as the Landsraad, but they do not seem to be engaged in day-to-day governance or lawmaking on the level of individual worlds. The empire is just too big to allow that. Therefore, interplanetary politics is feudal in nature. The conflicts that arise are between the rulers of worlds and they play out in terms of the control of fiefs or other macro-scale happenings.
2. The entrenchment of the class system (the "faufreluches") prevents the direct exercise of power outside of House leadership. 963
Specialists such as mentats or doctors are kept in a strict niche to limit their opportunity for common organization or individual advancement. Almost everybody depends on Houses (Minor or Great), and while a House may become stronger or weaker, alternatives to the House system are being suppressed. The exceptions, such as the Bene Gesserit, are still not viable avenues for change to the political system in general.
3. Disruption due to new technology and mechanization is consciously limited. In God Emperor of Dune, we also hear "Technology breeds anarchy. It distributes these tools at random." Religious taboo on AI also means that people value governance by heroic individuals. We see emphasis on training aristocratic scions, such as <PERSON> and <PERSON>, rather than developing governance systems that are less hierarchical.
4. Due to the development of shields, warfare is done by either infantry or atomics. And atomics are unacceptable to use. Military power thus relies peculiarly strongly on hierarchy and loyalty, whether by large bodies of troops or smaller elite forces. If they could win with heavy artillery then this would imply a more industrial society with a smaller number of soldiers, but as it is we are in a world of epic scale hand-to-hand combat.
A good deal of God Emperor of Dune is about escaping the trap of this model, called "the Pharaonic disease", of an overly-settled civilizational form dominated by the individual will of its leader. So space feudalism is not seem as a Good Thing in the text, just an empirically successful system that is difficult to displace once entrenched.
In that novel, an even-more-politically-aware individual,
! God-Emperor <PERSON>, millennia-old human/sandworm hybrid
writes:
Scratch a liberal and find a closet aristocrat. It’s true! Liberal governments always develop into aristocracies. The bureaucracies betray the true intent of people who form such governments. Right from the first, the little people who formed the governments which promised to equalize the social burdens found themselves suddenly in the hands of bureaucratic aristocracies.
That quotation perhaps gives some hint about whatever happened to democracy at a sub-planetary level. Elsewhere in the text, the same character asserts that most bureaucracies promote bad administrators, meaning someone "more concerned with reports than with decisions", whereas "The difference between a good administrator and a bad one is about five heartbeats. Good administrators make immediate choices." The thesis seems to be that liberal democratic governments develop established bureaucracies, which are easily converted into quasi-aristocratic systems (centralizing power into the ruling political caste). From there, successful players (those who act decisively and who "surround themselves with people able to act wisely on the basis of verbal orders") turn the whole shebang into an formalized aristocratic hierarchy. 222