Also, copper cables capable of transmitting high data rates aren’t easily manufactured either. Think of shielding, twisted pairs of wires, etc. And they don’t even contain a lot of copper.
This is because you (in theory) need the whole blockchain to validate an NFT, so you want to keep it as small as possible.
But since you store the Cryptographic Hash of the image too, you can validate that the image on the server is actually the same one referenced by the blockchain. You could even move it to another server, but it will break the link obviously