*sigh* Okay, one more time: Once Rockefeller had eliminated any institutional competition by crushing any upstart electric car companies (there were once hundreds of them) and destroying any hope of a comprehensive national passenger rail system, he had effectively hooked the public on his product: oil. To be fair, he had help from Firestone Tires because cars run on rubber while railroads run on steel. Once that competition had been eliminated, his work was done. Didn't really matter what happened after that; America was forevermore dependent on cars and the oil that runs them.
That's why monopolies are bad, and it had nothing to do with government. If regulators had acted sooner to reign in Rockefeller and Firestone, we might be able to get quickly and safely from New York to San Francisco on a bullet train today, and our cities wouldn't be choked by smog and traffic jams. Who knows? But considering all the unintended consequences of a monopoly-created dependence on finding increasingly difficult to extract pools of dead dinosaurs to run our vehicles, it's a shame they weren't stopped sooner.