The ratio of those two values shows, in my experience, that a lot of people are not very good at things they spend a lot of time doing, and are generally unaware of their own shortcomings
The average American spends 4.2 hours a week in the car. A typical 40 year old american has driven around 50,000 miles. For someone to continue to be bad at driving after that much experience, it must be a fundamental limitation on their capabilities for learning, thinking, or understanding. Drive to work any given day in Denver and you will see that a large number of people suffer from those fundamental limitations.
This article seems to present a world where most people the author interacts with can think critically about a complex topic, and are interested in learning or improving themselves. I wish I lived where the author lives, because I have had multiple jobs across multiple countries and never encountered an average population like the author describes.
4.2 hours a week in a car doesn't imply that any of that time is spent doing things that may make one a better driver (by whatever standard we're measuring this), it's just repetion of the minimal amount of driving skill that's enough to get you by.
If it's not possible to increase one's skill in anything without practicing things that are just on the edge of capability then no amount of regular, unsupervisied driving without any critique targeted towards improvement is going to help.
Something like 50% of college graduates in the US are considered functionally illiterate, despite an enormous number of opportunities for intentional practice; and despite presumably knowing, at least somewhat, of the benefit of attaining more advanced literacy. https://www.nbcnews.com/id/wbna10928755
When I think of poor drivers, I think their incentives to become a good driver are much higher. After all, their own lives and the lives of their loved ones are at risk.