I’m going to disagree with most of these comments. They don’t protect the prong so much as they protect the cord or other objects in the cords vicinity (painted surfaces, fragile surfaces, etc). The little plastic cap that covers tire stems on cars and bikes , while keeping it clean when installed, are primary to prevent chaffing issue on the inner tube whike shipped and stored; same thing with this prong shroud. They have holes in them as to not retain moisture I imagine.
Long story short, the prongs are metal and have corners. They are the strongest, “sharpest” thing in the box. The plastic isn’t protecting the prongs from us, it’s protecting us from the prongs.
I believe it’s to protect the prongs from getting damaged during shipping - and if the container gets rained on or something, it could provide some protection from that
I’m of the opinion that it’s just to improve the perception of package quality. I don’t see those cheap plastic pieces as keeping the prongs from accidentally warping or bending but I guess they could keep moisture away. I’ve never received a corroded set of prongs before their use though so my theory stands as they are upping the packaging visual aesthetics.