Why is smoking still prevalent in the lower socio-economic classes?

Decades ago, everybody smoked. Rich, poor, educated, blue collar. As the dangers of smoking became better known, and society started to reject it, it was the more affluent and educated to started the trend. It eventually crept its way down through the socioeconomic hierarchy.

Now most smokers are less affluent, less educated, and can least afford the cost of maintaining a habit. The only people who smoke are blue collar, poor, or from Marrero. So why do they still love them some cigarettes?