Interesting concept. From my quick reading of the bills introduced, they seem to be akin to the Patent & Trademark Office's "use it or lose it" provisions wherein if you fail to use the mark in commerce or fail to protect it against infringement it reverts to the public domain.
Part of this problem stems from the difference in the US of a copyright and a registered copyright. At one time you could assert your copyright by simply including the line "Copyright (c) 19xx by <some name here>" the "(c)" was required to secure the international benefits of copyright outside the US. If you wished to register that copyright you paid a fee, completed a form, attached a copy of the work, and sent the whole thing to Washington, DC. Some time later they sent you back a certificate good for a while with the right to renew for another period when that expired. If I remember right (and I have been wrong before) the initial period was 28 years. Without registering that was all you could get in in the US. Other than by researching it is impossible to tell if the company or person(s) that published the book registered the work.
Since automation came slowly to the copyright office (late 1950s) and then on a transactional basis only, there was not a push to capture the history until the next renewal. Over the years there have been many conversions from one file type to another, from punch cards to tape to disk, and in access languages and schemes. Therefore many of the copyrights have to be manually researched. This involves a great deal of labor expense. Often the possible value of the work is perceived to be less than the cost of this research.
It is an interesting problem.