Just my opinion
... but this is but one of a jillion bizarre stories that occur each day. There are a lot of people on the road today that should not be. Some of them may be OK to be there next week, and many will not. And don't think they are all over a certain age. Many are very young and all ages in between. I don't think there is a law that could be passed that will eliminate all those that should not be on the road, or even come close to really making the road safer.
This means that when your mom or dad has passed that point, it is up to you to step up. I did when I realized my mom couldn't see well enough to know if she was really in the correct lane or not. One drive with her & we took the distributor cap (secretly) off the car to save her life & others. Her car was "broke" for long enough that she decided not to go for renewal as she knew she couldn't pass the eye test and didn't want that embarrassment of the denial.
Now, how do you keep the crazy cousin that is 33 years old off the road that has no business being there??? Personal responsibility, or lack of it, has much to with some of this. Not wanting to give up independence has probably the most for those aging. That behooves us all to have a plan for our later years and hopefully the cognitive ability to be aware of when the time comes to take the steps in the plan.
For those without family to do that, as this person seemed to be, it should fall to the neighbors, community, church, etc to take up the slack. Expecting the "government" to do so unnecessarily burdens the many with unneeded laws. We should be willing to help/assist each other and many laws are totally unnecessary. However putting this in perspective, even if there was no one that took note that this person shouldn't be on the road, this is one of many tragedies that occur every day and although regrettable, things happen that we don't control.
And again, as I said at the start of this, just one person's opinion and I appreciate that all of you are entitled to yours which may differ.