The real reason that copyrights don't get freed up is that those who are still making money on old copyrighted works have the financial means to and actually do lobby zealously for protective laws. Those who own the copyrights on old works that are not making money often don't even know they own the copyrights in the works that are not making money. Even if they did know they owned the copyrights, they have neither the interest nor any monetary incentive to take the positive action that is necessary to dedicate their works to the public domain. They can do it if the owners can be found and can be persuaded to take the time and effort to release their copyrights. For years library associations, and to a bit lesser extent, educational institutions, have lobbied for limits to allow the preservation of old works, especially those whose copyright owners are doing nothing to preserve them. The best they have been able to achieve are very very limited protections which allow some research preservation by libraries and archives, but they just do not have the money to compete with lobbyists for the likes of Disney.