CT Phipps
Carbon Dated and Proud
Going to interject here but I personally don't think Bethesda has some kind of philosophy behind keeping the Fallout universe in a perpetual crapsack state such as "human nature prevents rebuilding of civilization".
That is the case in the settings they've shown, though.
They keep it in this state because that is what they think Fallout is all about as do their fans.
Chris Avellone believes that as well.
In a way they are right, Fallout is about society after the bomb, but as the games have show, society rebuilds. Sure, it is a slow painful process, having various problems such as the various raiders, mutants, and whatever mess the old world left behind such as still working robots and who knows what else.
The games show some societies rebuild but Van Buren also shows it's possible for societies to regress like with Caesar's Legion and Presper's plan to reduce it to nothing. Both Fallout 1 and Fallout 2 also show the potential for all that progress to be eradicated is possible to.
Some places like the Sierra Madre and the Divide will probably never recover, and neither the NCR or the Legion will probably take all of North America or the American continents, but the human society will rebuild unless something else resets it. (some cache of nuclear weapons such as perhaps BOMB space station, a disease, a new army or threat that seeks to make the ruined Earth its own)
Which are all possibilities and as we see with NCR and Caesar's Legion, the rebuilding nature may fail.
So no, Bethesda does not act on any kind of philosophy or reasoning here other than "Fallout should be about a post nuclear war North American wasteland"
Which nevertheless has the fact attempts to rebuild have failed in this world until the player intervenes.