That's not the main point in the series on chemical weapons though. The main point is that modern armies are mobile and well equipped ("the modern system") and

That's not the main point in the series on chemical weapons though. The main point is that modern armies are mobile and well equipped ("the modern system") and that chemical weapons are only well suited to stationary, fixed opponents that are poorly equipped. However, if you are fighting fixed position, poorly equipped opponents there are better and cheaper alternatives that pose less of a risk of self-harm (and war crimes). In both the posts about elephants and chemical weapons, the theme is the same: they are not useful nor practical given the circumstances so the states make the rational decision not to use them.