The older I get and the more experiences I have with people and their various vices, the more I'm absolutely convinced that most vices and addictions arise out of trying to "self medicate" some unfulfilled need your body has. Sometimes we learn that these actually have underlying medical phenomena (see ADHD people self medicating with caffeine via coffee consumption) but because of just how little we know and the long history of moralizing addiction, often times we don't know what's being medicated, and so we assume it's a moral failing instead. This might also explain why something like alcoholism seems to have a hereditable component. If the effect of alcohol fulfills some need your body has due to some sort of genetic / biological makeup, it makes sense that said need could be inherited in the same way anemia or any number of other conditions are.

In your case, I would imagine there was something your body needed that it got from cigarettes / nicotine that it was also able to get via the exercise and smoking, so the need to smoke went away as that need was filled elsewhere. That need could have been a chemical deficiency, but also could have been a mental need (like say, time to stop and think, which maybe you got via smoke breaks, and now also get via being in the water)