https://lotr.fandom.com/wiki/The_New_Shadow
> I did begin a story placed about 100 years after the Downfall, but it proved both sinister and depressing. Since we are dealing with Men, it is inevitable that we should be concerned with the most regrettable feature of their nature: their quick satiety with good. So that the people of Gondor in times of peace, justice and prosperity, would become discontented and restless — while the dynasts descended from Aragorn would become just kings and governors — like Denethor or worse. I found that even so early there was an outcrop of revolutionary plots, about a centre of secret Satanistic religion; while Gondorian boys were playing at being Orcs and going around doing damage. I could have written a 'thriller' about the plot and its discovery and overthrow — but it would have been just that. Not worth doing
I find that writing process fascinating. Begin writing about your world a few generations later. Find you've added some satanists and other assholes to it. Get upset because the world sucks now. Stop writing the story because it wouldn't be a good one to tell.
It would seem he didn't control his own sense of canon and direction. He just had a genuine vision of it all and it was either going to be exactly that or nothing at all.