If the art is digital how and the artist agrees that editions of the NFT represent a copy of the art how is an edition of the NFT not a copy of the art?
Because it's factually not. You can't get the art from the hash. It's one-way. That's the whole point, to create artificial scarcity and non-fungibility.
Since it's not actually a copy, there's no first sale doctrine license to the copyright, making it illegal to have a copy of the art unless you have a separate licensing agreement. And if you do have such an agreement, that's the thing giving practical value.
You and I can agree that a rock represents your car, but I'm still not going to pay you for it.
There is in practice no first sale doctrine for digital images; the first sale doctrine gives you the right to distribute your copy, not to make your own copies; and you can't transfer a PNG to your friend without making a copy. The first sale doctrine deals with the intersection of copyright with physical copies of a work.
This is why no one is buying and selling digital artworks, except using an artificial concept of ownership - a certificate. The artworld has done it with paper certificates for a long time; NFTs are the same thing.
> This is why no one is buying and selling digital artworks, except using an artificial concept of ownership - a certificate.
You seem confused. A certificate does not grant ownership. The reason nobody is buying and selling digital images is because producing an exact copy of a digital image costs nothing, which means it's irrational to pay for a copy of an image since you can make a copy yourself for free.
Because a "copy of the art" is a work of art that is the same as the original art and an NFT is not a work or art and is not the same as the original art. An NFT is a virtual token, than may or may not contain some metadata. This is not the same thing as the original art. Therefore it is not a copy of the art.
