> Specifically munitions that are considered illegal to deploy in war, but are apparently acceptable to deploy by police?

the reasoning for this is less exciting that you'd like. its illegal in war because war is anarchy, and ypu cant tell what chemical weapons an opponent is using, and so proportional response is the worst variation you can think of.

when theyre used by the cops, you know exactly what they are using, and there isnt a chemical weapon escalation worry