The Rim worlds are the latest results of terraforming technology, only recently settled, and raw and untamed. Out on the farthest edges of the system, life can be quite challenging, as the comforts of civilization common to the Core Worlds just aren't so here. Technology and power are far more expensive out on the outer worlds and moons, so folk have to make do without. People ride horseback, farm with handmade tools, and resort to entertainment that doesn't require electricity or batteries to operate. While some folk dream of the luxuries available on the central planets, others enjoy the freedom of open air and hard toil. In their own way, they're as stuck-up as the Core-Worlders, looking down their noses at soft folk who've never dug a ditch or mucked a horse stall.
While the Alliance government has a presence on the Rim, its grip is more than a mite looser here than elsewhere. Folk can't count on help coming right away (or at all), so they are accustomed to taking care of themselves and their own. Frontier-folk are usually armed, ready to draw at a moment's notice. Children learn to aim by shooting cans off a fence post. The lack of government interference and monitoring has made the Rim a haven for outlaws, outcasts, and shady business folk, as well as a middle class who started to feel like their own planets were getting too crowded for comfort. There is money to be made on the outer worlds, something plenty are just now figuring out.
Each world has a Governor, each moon a magistrate. As long as the general peace is kept and the proper reports are filed, such powerful figures may pretty much do as they please, least as far as the Alliance is concerned. Some government officials are good. Some not. Same here as most everywhere else in the 'Verse.
A citizen of the central planets who wakes up on a Rim world might think he's traveled backwards in time: people riding horses and shooting six guns. Yet, here and there, you can still find the technology of the 26th century, from Cortex access terminals to high-security bank vaults.