The short answer is "no". We don't actually know why it was never used. This question was asked extensively in immediate aftermath of the war. Everyone had prepared for gas warfare before and during the conflict, and Eisenhower was being warned of possible last-minute deployments of it until the final days of the conquest of Germany. But even through the war crimes trials, no one was able to get a clear answer. There are, debatably, a few better prominent hypotheses.

One) "Gas is not a good weapon" / "Gas couldn't be used to Germany's battlefield advantage". There are a few contributors to this vein of thought, the most famous being Herman Goering's claim that Germans had tried and failed to build a gas mask to protect the horses that provided the backbone of the Wehrmacht's transport. A more theoretical way of making the point is that gas is difficult to reconcile with mobile warfare, as its persistence harms mobility more than static defense. As Germany's great advantage lay in mobility, this would be a net negative for the Germans.

Two) "If the German's used gas, the allies could manufacture more of it". The German chemical industry was already heavily strained by the demands of war, and they understood that their capacity for producing most exotic chemicals was inferior to that of the allies. And since some of the key precursors to these agents were derived from petroleum, the allies would hold an enormous advantage due to the critical German oil situation. An important caveat to this theory is to note that the Germans had achieved a quantum leap ahead of the allies in chemical weapons technology by developing nerve agents like Sarin and Tabun. But this was all of the greatest secrecy. No one could be quite sure who had what. IG Farben executive Dr. Otto Ambros claimed (at his war crimes trial, casting some suspicion over this tale) that he had convinced Hitler in a personal audience that knowledge of Sarin was recorded in international patent documents filed in America prior to the war. So, Dr. Ambros claimed that the Germans should only assume that Sarin was available to all participants, despite knowing this was almost certainly untrue. Thus saving Western Civilization. The court still gave him eight years in the clink, so it is doubtful they were convinced.

There is a third hypothesis regarding "mutually assured destruction and strategic bombing capacity". Hitler was a sociopath who did not care about any specific person, but he did seem to have some interest in the opinions of his own people as he narrowly defined them. One of the strangest things about the Nazi war effort in the early phase of the war is that Hitler seems to have felt insecure about his own political position inside his country. It was not until the victory over France that he became generally quite popular among Germans. And similarly, he was actually afraid to implement rationing and halt the production of consumer goods for fear that it would upset the population. One of the most bizarre facts of the entire war is that the Germans did not adopt a "total war" economy and halt the production of consumer goods until 1942. Hitler actually seems to have been afraid of putting his population through too much hardship in the early phases of the war (though he did not blink at it later when there was no real choice).

The Churchill government made it clear early in the war that German use of gas in the field would result in RAF strategic bombers dropping gas on German cities. A politically cautious, early war, Hitler would almost certainly have taken note of this threat and its consequences. Then by late in the war, when the Germans were desperate, there was such a huge disparity in strategic bombing capability between the Germans and the Western Allies that the start of gas warfare would have resulted in the wildly disproportionate destruction of German cities. So in this way, strategic bombing and mutually assured destruction may have produced an environment where the Hitler never saw gas as being to his advantage.

But after expending all that wind. The answer is still that we do not really know.