My guess is that authors have relatively long-term returns on their books, while movies are known to generally make almost all their money in the first year.
Generally yes, significant revenue (for books but also movies and music) may happen several years after the first release/publication. Because… reasons you don’t always control.
Ok, but the goal is not to make sure that artists can derive every possible revenue but only to make sure that they get enough to for the creation to be worth it.
Given the nature of the cultural market (authors/original creation often gets a very small share of what the end consumer pays, unless they are also their own editors, producers and distributors), it’s hard to make it worth it without extending in time (and part of the idea is that some of the value you didn’t get while you’re living will get to your legacy, which is a deep motivation too).
Streaming revenue has no public attribution of fees to specific content, as far as I can tell. It is very much possible that a large fraction of that revenue is driven by (and attributed to) new content, the same way DVD sales were.
Yes, that is the question to which neither of us has an answer. Streaming deals happen as bundles, and my understanding is the opposite of yours: the old stuff gets thrown in as a piece of the bundle to help make the catalog bigger, while new content actually sells subscriptions. In other words, the back catalog has some marginal value to the streaming service (and the studio), but it's the new releases that actually sell subscriptions.
Releases of "The Mandalorian" got people subscribing to Disney+, and new seasons of "Game of Thrones" had the same effect for HBO, for example.
In other words, a bundle of 100 movies for $10 million could be attributed as "$100k per movie," but that's almost certainly wrong. More likely, that bundle is a combination of something like $5 million for one movie, $1 million for a few others, $100k for a bigger set, and all the way down to $1000 or less for the remainder of the catalog.
