It said war threat, not civilian threat. We have antidote in the field to quickly administer. Civilian populations wouldn't have that capability.
I disagree that antidotes in the field will suddenly take out all toxicity from a nerve agent, they will keep the afflicted from dying until they get better treatment...but there are still side effects..often from the antidotes themselves.
And you have to have a continuous ready supply of antidote. If one come under repeated nerve gas assaults miles from resupply what do you do then hmm besides hoping that your protective gear will hold out long enough?