I don't know the true reason "why"... but, it certainly made them easier to change when the old ones dried out or rotted away.
You could just remove the old half-hood and then hook the metal tab of the replacement over the notch at the rear of the body and set the new one down and in place by locating the integrated cable adjuster extension into the hole at the top of the body... and, all without having to actually take the levers off of the bike to squeeze the new pads on.
Of course, they were never tears at the bottoms - as with levers pushing at the lower edge of full rubber hoods. Plus, the harder rubber would never sag or stretch out of shape.
The rubber simply cushioned your hands and rounded off the tops of the levers when your hands rested on the tops. And, everyone wore gloves, anyway, so to wrap the entire body may have seemed a bit unnecessary... at the time. Maybe not such a bad idea, really.
My old Mafac levers are still among my favorites, and I've really never found them to be uncomfortable. On the other hand, I've found many others to be very awkward or even annoying regardless of how well cushioned they were... but, maybe it's just my particular hands. Perhaps levers with half-hoods are not ideal for grasping during a sprint, but on a Touring or Randonneur bike, where you are not often intensely gripping around the hoods, they seem just fine ~ of course, you seldom see those styles of bikes anymore.
Bob Hanson, Albuquerque, New Mexico
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Doland Cheung asked:
Is their any particular reason why Mafac chose half-hoods instead of
whole ones?
Doland Cheung
SoCal