Why Are Smokers More Likely to have less Education and Less Income?

More and more people are quitting every day. If it was easy for you to quit smoking, you probably would have quit already. But those who are still smoking are more likely to have less education, less income and are more likely to have a substance abuse problem or a mental illness. This does NOT apply to all smokers but this is the group that are having a hard time quitting. Is there a connection?