I'm having trouble finding the source (I suspect a brief in Eldred v. Ashcroft), but I recall reading that over 90% of books are out of print within 3 years of their initial publication. I've also seen claims that it's typical for heavily marketed movies and video games to make roughly half of their total revenue in the first week of release, though I'm not sure where to find the actual numbers for that, and it probably doesn't account for re-releases (DVD, "HD remaster", etc.).

edit: Based on skimming some numbers at vgchartz.com, it looks like the basic shape of the claim for heavily marketed video games is right, but the revenue half-life is more like three or four weeks.

Where authors make money from their books they make it within a few years of publication. Where they make money from an adaption of their book it can be decades later. For example, Philip K Dick wrote Minority Report in 1956 but the film wasn't made until 2002 (https://en.wikipedia.org/wiki/List_of_adaptations_of_works_b...). Lord of the Rings was written in 1937 and made in to the major films in 2001. More recently Game Of Thrones took 15 years or so before being adapted for TV.

Those authors deserve a decent price for the film rights to their work. 30 year copyrights would significantly change that.

> Lord of the Rings was written in 1937 and made in to the major films in 2001.

Although the rights that permitted those films were sold in 1969.

Film rights are a particularly interesting case where they get sold and traded around potentially for decades before something is actually produced, if ever.

OK, I'd say that argues for longer copyrights for adaptations than for the written book itself.

Though I'm not sure if that's feasible. Maybe the most use of copyright free books is adaptations?