Germany had a huge stockpile of poison and nerve gas, but none of it was used. Why?
Not a response to the key question of “why”, but something I happened upon in reading James B. Lamb’s The Corvette Navy earlier on today that at least partially addresses the topic of the question:
Tales of such men, of those who lived, those who died, filled the reminiscences of corvette crews ashore. There was the haunting story of men plucked in good health and spirit, from a sinking ship by the escort [HMCS] _Minas_. Not long after they had been taken aboard, a couple of men began to cough, to struggle, to fall into delirium. In a matter of minutes they lay dead, and it was only then that talk began about the cargo their ship had been carrying: containers of poison gas for storage in the U.K. for retaliatory use in the event of a Nazi gas attack. Somehow, the torpedoing had loosed some of this fearful gas. Into the eyes of the remaining survivors came the look of dawning realization as coughing began among still others -- they were all doomed. Winin hours the last one lay cold and stiff. _Minas_, who had rescued a joyous party of live survivors, steamed on with a cargo of corpses.