There's a substantial economic literature on this topic.
Among other factors: time value of money and future-value discounting mean that economically ever-expanding copyright terms offer virtually no present-value benefit.
Most works see virtually all of their economic value in the first few years of publication. There are some (rare) long-tailed exceptions. The original US copyright term of 14 years, with extensions, actually fits the economics pretty well.
What extreme copyright duration does do is:
1. Create vast copyright-holding monopolies, often of works for which authors were poorly compensated if at all. (For the latter: academic publishing.)
2. Create a vast category of "orphan works" which aren't or cannot be published, in the latter case because rights simply cannot be clearly established, or competing claims (survivors, estates, publishers) exist.
Among other factors: time value of money and future-value discounting mean that economically ever-expanding copyright terms offer virtually no present-value benefit.
Most works see virtually all of their economic value in the first few years of publication. There are some (rare) long-tailed exceptions. The original US copyright term of 14 years, with extensions, actually fits the economics pretty well.
What extreme copyright duration does do is:
1. Create vast copyright-holding monopolies, often of works for which authors were poorly compensated if at all. (For the latter: academic publishing.)
2. Create a vast category of "orphan works" which aren't or cannot be published, in the latter case because rights simply cannot be clearly established, or competing claims (survivors, estates, publishers) exist.
"Seventeen Famous Economists Weigh In On Copyright : the Role of Theory , Empirics , and Network Effects" <https://jolt.law.harvard.edu/articles/pdf/v18/18HarvJLTech43...> (2005)
"The true impact of shorter and longer copyright durations: from authors’ earnings to cultural creativity and diversity" Jimmyn Parc & Patrick Messerlin (2020) <https://www.tandfonline.com/doi/full/10.1080/10286632.2020.1...>
Orphan Works: <https://en.wikipedia.org/wiki/Orphan_work>