Lack of raw materials? Some worlds may have different makeup than our nickel-iron core. Most important would be lack of water and above all:
THERE IS NO PETROLEUM IN THE VERSE.
The worlds of the Verse had no carbon based lifeforms before terraforming. Therefore no oil. Therefore no plastics, cheap fuel, coal, gasoline, etc. Not even paraffin for wax candles or polyester for clothing and other fabrics.
And further, wood would be an expensive product since it takes 25 years to grow a tree to harvestable size. Bamboo would be the easiest substitute. On a newly terraformed world, houses would be built of adobe, brick,stone and metal (locally mined or imported).
DH and I were discussing this the other night in terms of transportation. Roads would have to be concrete. Personal vehicles would be rare, although those that existed could be very high-tech -- for example the hovermule that the crew uses in the BDM. The train in the Train Job would be normal for middle distance travel combined with air(nuclear fuel cells?) for long distance. That Serenity, a cargo transport, can be flown in atmosphere as well as in the Black is an indication of this delivery method.
I work in Canada's Department of Aboriginal Affairs and Northern Development. The difficulty of developing infrastructure in rural and remote communities should never be underestimated.
And it is canon that a program of homesteading is still underway for Rim worlds. For comparison take a look at a few episodes of Hell On Wheels, where occasional "high tech" buildings (such as a very high class and well finished hotel) show up even ahead of the railroad, although the surrounding land is either subsistence farming or held by the local First Nations people.