Carved pumpkins are an important part of modified minecraft gameplay, especially using the CustomModelData feature, which makes carved pumpkins the only item that can be used for custom headwear. Because the Elytrian origin cannot wear them, it greatly diminishes players' possibilities in unintended ways. Since it doesn't add any armour points, there is no reason not to allow it, since behaves as if the player didn't have any armour on their head.