". . . because that would require a legal acknowledgement that they are Ansel Adams images."
The LAT's Mike Boehm points to an interesting Catch-22 in the story of the newly-discovered "Ansel Adams" negatives: if they really are by Adams, then it's a copyright violation for the guy who found them to make prints from them. But to bring a copyright infringement suit, the Adams' estate would have to concede the negatives are in fact by Adams!
If you're late to this whole story, Lindsay Pollock has the Cliff Notes version.