Good point. But "fairy low value" doesn't equal to "completely useless", an example would be the photographs on Flickr, it was the largest collection of photos

Good point. But "fairy low value" doesn't equal to "completely useless", an example would be the photographs on Flickr, it was the largest collection of photos available under the CC BY license, and at least Wikipedia was one of the largest project being benefited from it. Also, I could publish my work under the Sunset License before I permanently license a copyrighted book/research paper to a Big Publisher, because the license is non-revocable, the license can effectively prevent the publisher from locking it up forever, without some possible objections when using CC-BY or CC-0.