Because most people are too stupid to do what I did, as early as 1987. Keep an eye on gas mileage. I was a good patriotic Iowegian, who did the patriotic thing, and filled up with crapohol at my local FS station. I watched my gas mileage immediately go from 20 down to 15. I thought something was wrong with my car. After a few tank fulls, for whatever reason, I went to another station and put pure gas back in my car, and my gas mileage immediately returned to 20.
Face it. Most people in Obama's America are too stupid to notice such a thing.