Apple was clearly thinking outside the category of “consumer electronics.”
And even if one does, then you just consider the diminished value as another cost of having the personalized item.
For many people, especially gift givers where the item is about far more than economics, it is worth it. And it is very unclear to me why "resale value" should trump about a million other considerations.
Then recall that premium silver, especially items given as presents, are very often engraved, and have been for hundreds of years.
Apple is a premium brand, not "any other company," especially in the era this post covers.