When you buy new electronics & appliances, there is sometimes a plastic cover on the AC power plug. Is there any point to those? Are they just to protect other items in the package from being scratched by the metal, or is there any electrical safety reasons? Or is it strictly for marketing, to give the impression of a high-end, well-packaged product?
Cosmetic protection.
I think it’s just to prevent scratches, as you say.
I’d think also to prevent the prongs from being bent in transit.
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It keeps the prongs from being accidentally bent (thus there is a bit of a safety aspect).
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It keeps the prongs from scratching other things (packaging plastic, the item itself, etc.).
The covers are included on UK 3 pin plugs, and they can’t be there to prevent the pins being bent in that context. The pins are not remotely bendy - in fact, the covers are very thin and flimsy compared to the pins.
So it seems like it must be to protect other things from being damaged by the pins - maybe while the appliance is on a production line and the flex with its fitted plug is not exactly flapping loose, but is not packed or secured away.
However, the covers also appear on the plugs on packaged IEC leads - which are typically bundled and bagged separately from everything else in the box, so there’s no risk of the pins scratching anything there. Doesn’t really make sense.
The wires have the plug molded in at a shop not remotely connected to the place making the appliance.
The wire makers have no idea where/how that particular cord/plug is going to wander before finding a home.
If a $0.05 cap makes the appliance look “upscale”, your cord/plug may get better reception than those made by a competitor who doesn’t provide the cap.
When your product is a “line cord, 5’, US/CAN/UK/wherever”, any differentiation is a plus.