The Germans didn't use chemical weapons because they didn't want it used to them period.
They didn't drop Serin Gas on the UK, because they didn't want the UK to respond in kind. It is the same reason why there wasn't the systematic torture and execution of our POWs.
True. It doesn't change the fact that misinterpreted photos made them think that we were better prepared than we were to respond immediately.
Not that we didn't have the means to respond in theater. We did not have nerve agents, but a freighter full of blister agents was hit by German aircraft in an Italian port, with tragic results.