The problem is everyone thinks they're a legendary driver (well no is going to to turn round and say they're a below average driver are they?)
But truth is, most are average and some seriously below.
We are all human and all subject to mistakes.
RAC data shows 83% of drivers would NOT pass today's driving test, it has changed drastically over time - the next change is that it will include the use of the satnav on the test.
But the most major problem is that for most people, once they pass the test they think "right that's it, no more learning" truth is you should NEVER stop learning to drive, cars change, road rules change etc. Be honest, how many people have even picked up a highway code since their learner days?
The government has looked at re-testing so many times over the years, but it would be logistically impossible,
Not enough test centres, not enough examiners (and the test fee would not cover all the investment needed to train up extra staff at DVSA) and the government won't invest.
Also the wider implications - say someone is retested and fails, but they rely on their car for work? They can no longer do their job, so could lose the job, etc - It just at the moment is logistically impossible.