> Is there something here about the role of (and lack of in this case) deliberate and intentional practice?
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.
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.