Why are you using past tense?
It is still very much legal to sell and use leaded gasoline. The reason: If we remove lead from gas, it's hard on the engines.
Think about this for a minute. Society is putting the health of a machine over the health of people forced to breathe the poison being spewed into the air. And coal fired plants are no different. They are allowed to spew tons of lead and other toxins into the air and operators of said plants get away with crying about how much it would cost to remove the lead from the smoke stacks.