>>64270487
The destruction of san Francisco was followed by the NCR-BOS war that led to both of them being reduced to near nothing
The NCR technically won but they were so devastated by the war that they abandoned all their territory and what was left was immediately seized on by caesers legion
The sole remaining NCR town you can visit in van buren, hoover dam, mentions that they havent heard from shady sands and are unsure if it even exists, they are effectively a sovereign state
The west coast would have been reduced back to a scavenger world even harder than it is in the current game

The destruction of san Francisco likely had more to do with them just feeling rather strong negative emotions to the entire place being a chinese stereotype with scientologists living nearby
Rather than quietly retcon the place to have always been a sane, non-stereotypical, city and lo pan and the dragon just being hallucinations of a chosen one, they would rather nuke the place

Also why they killed off all the talking deathclaws and wanamingos
JE sawyer tends to just kill off parts of the setting he feels dont fit in