Well honestly people were in vaults most of the time after the war so they haven't had that much time trying to get civilized. And also nuclear blasts would destroy most outside life and radiate most water on the planet, so being civilized would be very hard. You would need constant protection and constant flow of money to survive. And if a society has all this in a post nuclear war wasteland, they will REALLY fight for it.
No, that's no excuse.
The people outside Vault 101 never got into a vault, they have had 200 years to built that hunk of junk.
Plantlife does not go bye bye by radiation, look at Chernobyl, after some plants died off the rest thrived in the radioactive glow.
And water, rain, is not irradiated, it's not hard to take a bunch of buckets and place them out in the rain to collect water.