Everything outside in the wasteland is a representation of slums, and battlefield. And people that have knowledge and resources are those that live in vaults and Brotherhood. Those are the places, where everything is clean and tidy. It was the main premise of first games, that Brotherhood of Steel is the last refuge for humanity, and everything else is mutants fighting with sick,hungry, degenerated people - simple, comicbook style plot with heroes and villains.
And for the 100 time, people do not rebuild during war, they do it after. Wasteland is at constant war with mutliple factions, you don't build a concrete house, if you know that few months later it will get blown away, and you will be covered in rubble. No one rebuilt anything during WW2, people lived in ruins back then, why would it feel unreal to you? People were hiding on the streets in trash, doing diversions and sh*t, it is all there in history books. Look at WW2 photos and tell me how tidy it was, they were hiding in severs, and again - no mutants trying to kill for no reason, no mutated pigs. It is not like a bottleor a scrap is lying there for 10 years and no one is cleaning, stuff gets wrecked every day, and every day new trash and new holes in the wall are made. I don't understand why it is so hard to believe in, it shouldn't be anything that causes disbelief, there are lots of worse, illogical decisions Bethesda made that ruin it for me, but I will defend the way they see society.
People here have presented a lot of solid arguments against OP claims, but you seem to be reading only what fits your view, and ignore everything else.