What is probably the main reason that atomic bombs were never used in the Cold War? They were too expensive

It took too long to produce them

Once one side used them, the other would as well possibly ending the world

It ruins the territory its used on making it pointless for wars of conquest

Once one side used them, the other would as well possibly ending the world

Explanation:

The Cold War was basically a game of "Who can intimidate each other with a bigger atomic arsenal?". Each side was fearful of the first pulling the trigger with nuclear weaponry, and they didn't want to be at an arsenal disadvantage, so both sides stockpiled a lot of weapons. Nuclear weapons are horrifically devastating, so if the Soviet Union and United States had started launching them at each other, it could have possibly led to an extinction level event.