Well That Explains It
NASCAR is still permitted to use leaded fuel. The lead particles emitted by these engines cause neurological damage: NASCAR makes you STUPID. It may not be nice, or kind, but it is a scientific fact: going to a NASCAR race lowers your IQ through lead poisoning.
Well, we can't outlaw leaded fuel for NASCAR because it would cost the teams money to redesign their engines, unlike millions of American cars that have already been converted.