It’s probably not for shipping of the final product at all. Cords for a product are going to be purchased in-bulk. There will be thousands of these cords with sharp and semi-fragile ends all packed together and then handled throughout the product build. This cap both protects the prongs from shipping/handling/assembly processes and protects equipment/handlers while products are being assembled. There’s no good reason to remove the cap after assembly, so it stays on the final product to the consumer.