I was a non habitual smoker for years and did it for the social connection. I also smoked habitually for a year and stopped. I'll likely continue to smoke with a friend or stranger under the right circumstances, but I don't want it to be every day or even once a week.

I'm not advocating others smoke, nor am I saying this is a reason most other smokers do. The GP's claim was simply familiar and valid, which is why I'm sharing.