The infringement can go in both directions though. The fanfic obviously infringes Tolkien but it's not so obvious that Amazon doesn't infringe the fanfic. Tha

The infringement can go in both directions though. The fanfic obviously infringes Tolkien but it's not so obvious that Amazon doesn't infringe the fanfic. That was a common scenario with unsolicited scripts for TV shows. Some Star Trek viewer writes a script where the Enterprise is turned into a pumpkin, sends it to Paramount for consideration, Paramount says no thanks. Next thing you know there is a Star Trek episode with the Enterprise being turned into a pumpkin and oops, the amateur scriptwriter sues. The script is a work derived from ST, but the episode with the pumpkin is potentially derived from the slushpile script. So now there is a fight about whether Paramount developed the idea independently. For that reason studios are very careful about exactly how and when they will accept script submissions from outside their usual stable of writers.