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.
> it must be a fundamental limitation on their capabilities for learning, thinking, or understanding
You said it yourself. Assuming people are doing something without being mindful and purposefully trying to improve then 50k miles on mental autopilot it is not a surprise that someone wouldn't get better at driving. Without a desire to improve and/or being involved in a process that would give feedback then there will be no growth.