Healthcare...?

I have often wondered and have become increasing perplexed by the number of Healthcare professionals that smoke.
My workplace is a huge example and it makes me worry/giggle at the same time. I have never smoked, so maybe that is why I just don't get it. But as healthcare professionals and knowing even more so the dangers of smoking 1st hand, why do they do it?
I think it's just for the 15 minute break, which is also sad in its own right!