The early history of leaded gasoline

[Laconian]

https://www.smithsonianmag.com/smart-news/leaded-gas-poison-invented-180961368/

We could've spared millions from lead poisoning by going with ethanol as a knock reducer, and the bigwigs knew it. "...But from the perspective of GM, Kitman wrote, ethanol wasn't an option. It couldn't be patented and GM couldn't control its production. And oil companies like Du Pont "hated it," he wrote, perceiving it to be a threat to their control of the internal combustion engine."

[MX793]

Lead also helped as a lubricant for valves and other parts.  I also don't think it attacked rubber parts (seals and hoses) or fouled up carburetors like ethanol is prone to.