Is there a common reason that everyone smokes?

Everyone doesn't. 50 years ago almost half the population of the us smoked. Currently, fewer than 20% of the population smokes cigarettes, depending on male/female and geography a bit. Nicotine is a very reinforcing drug, and tobacco companies know how to entice people with advertising how sexy and masculine it is. It is the number one cause of preventible death and illness in the world, obesity is runner-up.
1. Nicotene addiction is the major reason that people cannot quit smoking. Although nicotene does not make you sleepy or have an accident while driving, it is still one of the most addictive substances we know. It is very hard for many people to stop smoking due to this addiction. Some people have add, and nicotene acts like one of the add medications. These people need to seek treatment.