I recall some years ago hearing about the "copyright cliff" from some informal research that was done related to Amazon listings. In an effort to turn up that research again, I ran across this (much more formal) treatment from Berkeley Law. The basic idea is that publishers aim to maximize profit, which means focusing energy on publishing the most profitable works. As the terms of copyright have increased, it has also increased the number of works that remain under copyright, but are unpublished and unavailable. Accordingly, the researchers found a negative correlation between copyright and availability: works that are still under copyright are more likely to absent from store shelves.
This is interesting because it's a good example of a cost to society that is difficult to measure, and therefore gets ignored (McNamara Fallacy). It very much reminds me of how other industries can externalize their costs onto society in areas where money isn't a good measure of value.