Why is a Van Gogh more valued than a photocopy I made of a tree?
Not sure, is it? I guess you could sell a photocopy you made of a tree, while Van Gogh failed to sell most of his paintings. Famously, the Portrait du Docteur Rey was used to close a chicken coop for a decade because it had absolutely no value. Yet it contained the same amount of human expresssion back then.
Or, more simply: why is human expression valued?
If it is inherently valued, it is valued the price of a chicken coop's door. The remainder of the value must come from elsewhere.
I'd say it's
the effect it produces on the viewer (beauty lies in the eye of the beholder) that makes a large part of the value assigned to an artwork. How it is produced can affect this reaction, with some disliking paintings or photography or photoshop or AI), but it might not be the main drive for appreciating something, nor something that's taken into account by each and every potential enjoyer.
Some might focus on the end result only to generate this appreciation (and disregard the details on how it is done), and I guess they wouldn't be the ones to buy Zone de sensibilité picturale immatérielle* by Klein nor Friedman's 1000 Hours of Staring**.
* = It's a non-existant area you're given a deed to. Optionally, you can complete the artwork by destroying the non-existant area and throwing it into the Seine in the presence of an art critic or a museum director.
** = it's a white sheet of paper the artist (purportedly) stared at for 1,000 hours.
Then there is the speculation value. If it was only the
human expression that is valued, a lithograph made by an artist and signed by him wouldn't be valued much less than the original proof, and the lithograph numbered 5 wouldn't be worth more than the lithograph numbered 83.