They picked lead because it was the cheapest additive, not because it was more profitable for the industry as a whole. Those two things aren’t the same. In the oil industry, the products are identical and companies compete only on price. If you use the $0.10 per gallon additive when everyone else is using the $0.05 per gallon additive, then your sales collapse because customers just cross the street to save $0.05 per gallon. But if every company switches to the $0.05 gallon additive, that doesn’t mean the companies pocket the extra $0.05 per gallon. Most of that goes to the consumer, because, again, consumers can just cross the street to get the better price.

It’s really a collective action problem. Nobody wants their gasoline to be more expensive than other companies’. So everyone has the incentive to use the cheapest ingredient. If you ban that ingredient, prices go up. But since everyone's prices will go up, you remove the competitive disadvantage.