This isn’t always true. People collect stamps with postmarks on them as well, that can’t be reused. Stamps without postmarks are generally worth more. But if a rare stamp only has examples with marks, it will still be worth a lot, but useless to post a letter with.
Still there is scarcity because these are physical objects, most of which are out of production. With NFTs you don’t buy a thing, you buy a link to a digital representation of… something. If the creator of the NFT decides to stop hosting that link your NFT is not only worthless it is also gone.
This isn’t always true. People collect stamps with postmarks on them as well, that can’t be reused. Stamps without postmarks are generally worth more. But if a rare stamp only has examples with marks, it will still be worth a lot, but useless to post a letter with.
Still there is scarcity because these are physical objects, most of which are out of production. With NFTs you don’t buy a thing, you buy a link to a digital representation of… something. If the creator of the NFT decides to stop hosting that link your NFT is not only worthless it is also gone.