Why do people smoke?

Having never been a smoker I'm sure I really just can't understand it; but really what is so appealing? I recently sat in a room next to a smoker for an entire afternoon and I could hardly concentrate on the key note speakers because I was so distracted by the ash tray sitting beside me. Perhaps I have an ultra sensitive nose? Or maybe I just let the annoyance build and build and held a grudge (likely), but really, I just think this person smelled. This made me think of all new questions: Do smokers know they smell? Maybe they know and just don't care? Granted not all smokers smell to the same degree, but they still all do smell somewhat. I don't get it.

You would smell better, have more money and likely live longer - what's the down side to NOT smoking?