Welcome to the real world.
I remember some years back a work friend who used to give me a lift back after work her car was in a torrid state, it only just about ran, and I asked her if she was planning to get it fixed, and the reply was as long as she can get from (a) to (b) it is good enough, this was my first job in a factory, and its a case of spend the minimum on a used vehicle, only pay to pass a mot or if it stops been able to do what you want it to do when you on a low income.
I do agree that for safety reasons driving assessments, probably need to include safety related car maintenance skills, and maybe they do now, but the fact I didnt know what the tread depth should be on a tyre, is not an outlier, it will be the case for the majority of people, as has been said in here, non enthusiast's generally treat their car as a white good.
Can see similar on social media as well, occasionally people will post about a problem with their car and ask for help on might be wrong, they show a demonstration, and often the warning light will be on and one wonders if they carry on using their vehicle routinely with it on simply because they cannot afford to do proactive maintenance on their car.
I am surprised tech hasnt been used to assist on this e.g. install brake pad sensors, when it detects too low, it then limits the speed of the vehicle until its fixed.