Rivers of digital words have been written on the fact that Bethesda does not understand this. For the Bethesda writers the apocalypse happened always a generation ago. One, two centuries may have passed but people will keep living in ruins exchanging bottle caps because the world needs to stay sterile and in a fake-post-apoc-50ies stasis. Because it's easier, because it's what people recognize. The Brotherhood is the most triumphant example: they went from major faction in 1 to minor appearance in 2 to tragic parody of themselves in FNV, but the Bethesda fallouts needs a Paladin/Army equivalent so they resurrected them and made them a center piece. Because Power Armour is what people recognize, and god forbid doing anything else.