I'm just explaining why buildings are broken down and in disrepair rather than demolished like DC or the west. Still doesn't explain why only 1 bomb landed near Boston, Idk if there's an ingame reason for that, you'd think hundreds of nukes would land on the city rather than just 1 outside the city.
With a 750kt nuke (megaton nukes were retired in the fallout universe and most nukes used were 200-750kt as stated in the original Fallouts manual) everything and everyone in a 12.3km2 radius around the bomb is pretty much destroyed, past that up to a 54.4km2 radius small residential buildings...
Nuclear bombs affect a large area. The city just wasn't totally levelled like D.C or the west because no bombs fell directly on it. It's still pretty bad though.