Maybe a more targeted approach where every driving conviction leads to a retest however minor. 10 years is. Along time for a bad driver to remain on the road. A driving conviction is proof your driving is below the minimum standard. And doesn't burden the good drivers. With unnecessary tests and may encourage the bad drivers to up there game. This strategy would lead to 2.4 million retests a year but would hopefully reduce as the bad drivers are weeded off the roads.
People will just 'drive for the test' during the test, as largely happens now, then go straight back to driving as they normally do, and are normally allowed to, in general.
Enforcement on a regular basis is far more important and effective method than a largely bureaucratic exercise of very limited effectiveness.
It doesn't matter as much, now that Brexit has buggered up the use of UK licences by those holders resident in other countries, but, until recently, this proposed 10 year retesting system would have invalidated licences being used by people living 'on the continent' and with no easy access to a UK test centre.