There is a legal zone called the public domain which consists of things like comics, movies, etc., that anyone can use for fun or profit. These works are ones that no longer fall under copyright regulations. However, copyright laws are more complicated than that, and this is not a site about laws. Instead we will be talking about why we need a more focused listing of public domain comic books.
The first reason we need a single resource for finding public domain comic book titles and characters is for those creators who wish to explore them. Two comic books that have used this method are Project Superpowers (2013) and Savage Dragon #141 (2008). In the case of the former, a revisionist reimagining is done to both update and reintroduce various public domain characters. While in the latter, a mostly visual introduction is given. Also both Project Superpowers and Savage Dragon (1992-Present) give an explanation of why the public domain characters disappeared in their respective universes.
A second reason for having just one main listing is that for scholars, fans, and others to know what is actually no longer copyrighted. In the case of scholars and lawyers, it would be for research purposes. For fans, it could be a simple desire to become more knowledgeable about comics.
Finally, this undertaking is important for those wishing to make money, reference, or find some other use for comic book properties without legal problems. One example of someone who has gone both the money and reference route is comic book reviewer Lewis Jeffrey Lovhaug, alias Linkara, the host of “Atop The Fourth Wall”. He has created for-profit DVDs, such as Atop The 4th Wall Vol. 2.5 Special Holiday Issue, containing reviews of Public Domain comics. Also, he often uses visual references from comics in his reviewing process.
In the end, though, it just makes it easier for people and corporations to stay out of each others way if a list were to be created.