The big problem with repeat tests at regular intervals is simply the resources required to do it. If you pass your test at, say, 20yrs and then have to retest at 30, 40, 50, 60, 70, then that needs six times as many examiners/test centres as we currently have, possibly more since the number of younger people taking driving tests is reducing.
I'm not sure it would achieve a lot to be honest, the biggest problem with road manners is attitude, and a test won't change that in many people.