Smoking and littering

So I have been wondering something for a while. Why is smoking not considered littering? I guess that I have wondered this since I did some community clean up work with the school. When we went out and picked up trash, a lot of it was cigarette butts. And those things are nasty. Who knows where they have been. But we know where they are. All over the streets, sidewalks, entrances, etc... They post signs on the freeway for littering, but no one ever gets fined for flicking a butt out the window. I do not like it when I am driving down the freeway and a cigarette comes flying out of the window in front of me. It may be because I am always nervous the ashes will jump up and hit my gas tank. Forgive my weird paranoia, but that really does go through my head.
Everyone knows that smoking is not healthy for you. That is why the government raised the cigarette tax. They want to get rid of smoking because it costs the country billions in health care each year (no source on that, may be an exaggeration, I am not sure, either way it is close). So why not start fining smokers every time they litter too?