40 years ago, giant entertainment companies embarked on a slow-moving act of arson. The fuel for this arson was copyright term extension (making copyrights last longer), including retrospective copyright term extensions that took works out of the public domain and put them back into copyright for decades. Vast swathes of culture became off-limits, pseudo-property with absentee landlords, with much of it crumbling into dust.
After 55-75 years, only 2% of works have any commercial value. After 75 years, it declines further. No wonder that so much of our cultural heritage is now orphan works, with no known proprietor. Extending copyright on all works – not just those whose proprietors sought out extensions – incinerated whole libraries full of works, permanently.