The value of pokemon cards or birkin bags is not because they are physically owned. This should be obvious from the fact that I could cheaply reproduce them and my identical reproductions would have 0 value compared to the original. I still own them though so again, according to your reasoning they should have the same value.
Some pokemon cards are worth so much i could reproduce them with gold instead of cardboard and it would be worth less than the cardboard version (assuming the same weight)
Things can have value beyond their physical substance. A Pokemon card isn't just paper and ink. I'm not arguing about whether the asset has value, I'm arguing about whether you actually own it.