Because the NFT isn't the t-shirt. You can own the NFT and the physical t-shirt, and sell the NFT to someone else but give them a fake t-shirt. They don't suddenly have a real t-shirt just because they have the NFT.
> You can own the NFT and the physical t-shirt, and sell the NFT to someone else but give them a fake t-shirt
That's a very smart way to achieve nothing. You now have created an actual copy on a shirt, at your cost, and proceeded to still own a shirt that has no market value now that you don't have it's authenticity proof. Seems like a very smart thing to do.
NFTs were created for the very reason that certificates of authenticity have no value unless the ledger from which they were issued is not public.
How can you know there wasn't more certificates printed than tee shirt created ?
How do you know it's a real certificate in the first place ?
How about you loose the certificate ?
Seriously there really is no reason to not prefer a digital certificate versus a physical one, it is on all accounts superior.
You certainly wouldn't argue cryptographic keys are useless because we have physical ones on any other matter if it wasn't for following the "I don't like blockchain" trainwagon.