The rules for renewing your driving licence over age 70 are ridiculous, IMO. There should be some kind of in-person medical fitness/reaction time assessment, and if possible a scaled-down driving test if any major medical issues are flagged up.
My parents are both nearly 80. My father has not driven for nearly 15 years following an illness which left him partially paralysed. He can now walk again, but has limited strength and mobility in his legs. He has also had strokes, heart attacks, a pacemaker, diabetes etc. He is mentally alert but his physical strength and reactions are nowhere near adequate to drive, not to mention being totally out of practice, but he recently insisted on renewing his driving licence 'just in case' and had no problem doing so. Crazy. He would be a danger on the roads. Luckily, he has no intention of actually driving, as far as I know, but no one could legally stop him if he decided to.
My mother is the same age, has different but equally severe health issues, gets anxious and easily flustered, and last drove about a year ago, but she also has a current, recently renewed driving licence.
My parents live in an area with no public transport, and get by with me and others doing shopping and driving them to appointments, and they can afford taxis when no one else is available, but if they had fewer people to help or less money, I can see that they might be tempted to drive short distances to shops, doctors etc.
It really should not be up to them to decide if they are fit to drive, and it should not take a potentially fatal accident to stop other people in similar states of health from driving.