The point of the learners is the theoretical so you can start practicing, how exactly are you supposed to practice without driving?
And near everyone I know first learned to drive somewhere in an unused parking lot for a couple of hours, not on the road.
The learners stalling on the road are stressed because e.g. traffic is moving and they are still trying to do all the K53 checks etc. and it will take a while before they can do that smoothly. There really isn't a problem with that system currently in most case and I haven't heard of any bad accidents being caused by it, just traffic hold-ups, which won't be alleviated by forbidding them to drive on the road.