Tolkien only died in 1973. Most of the work that would be more appropriately adapted here was published posthumously with Christopher as the editor/copyright holder. He died 2 years ago.
Even with a shorter copyright term most of this would still be under copyright.
I’m not sure Amazon having a tougher time on a cash grab is a great argument for shorter copyright terms. The Tolkien Estate has been generally a good example of how to manage a copyright in this system. They haven’t shat all over to make a lot of money. Christopher legitimately did serious, academic work from his father’s papers. They haven’t been overly litigious. And when they have stirred legal shit it’s been against major companies. Not fans, parodies or small operations. The fact that D&D exists as it does today is evidence of that. The only conflict there was early use of “Hobbit”, they still roll with the also Tolkien derived “halfling” and got away with cribbing his entire conception of Dwarves.
ETA: The most prominent dispute was with WB/New Line. In part over their assumption that they were clear to make whatever videogames they liked, despite not having rights for that. Because they claimed video games were just merchandize for the films, which they did have rights for.
The estate wasn’t even pissed about the various games. It was the slot machines that had them mad.
From a February Vanity Fair piece.
So what did Amazon buy? “We have the rights solely to The Fellowship of the Ring , The Two Towers , The Return of the King , the appendices, and The Hobbit ,” Payne says. “And that is it. We do not have the rights to The Silmarillion , Unfinished Tales , The History of Middle-earth , or any of those other books.”