For consistency, I suppose that both flying and driving would conduct the some form of skill test *before* solo, then have further supervised solo and perhaps a second test before award of a licence. Actually we do, as the unrestricted FI qualification includes an implied competence to authorise solo flight.
I could certainly see arguments for that, and in flying we'd probably accept it, but in driving I'm pretty certain that a lot of people would scream blue murder about it.
G