These are worlds that are just starting to be colonized, such as the Wilds.
Here human labor, even transported through space, is much cheaper than machinery. Most colonists come over on contract with various companies. The companies themselves deal in raw goods such as lumber, coal, metal ores, etc. Although riches are promised, these companies are essentially the law in their own little towns. Most workers are lucky to break even at the end of their contracts since the companies charge for housing and tempt them with expensive luxuries such as alcohol.
Each of these worlds comes with their own unique challenge. Many of the lower worlds are mining colonies. The Wilds are unique for being a source of lumber, coal, and organic material as well as holding valuable minerals.