Well, to be fair, destroying The Ring was always the main objective of the quest, and the defeat of the evil demigod Sauron was intimately linked to that. All the talk about the ancient Men of the West who were descended from the Kings of Gondor and how the Rangers were rumoured to be them in hiding or exile or whatever, seemed a secondary plot at best, and mostly just backstory for us, and I think JRRT meant it to be that way. As the story went on, it did seem to come up a bit more often, but it still felt like it was just to give us more background on the whole deal with Gondor and Rohan and Denethor and Theoden, and who the Stewards are and why they're not Kings, and again it was easy to dismiss because the big war was coming up, and Frodo and Sam were in Mordor now, etc. And oh yeah, those giant flying things that can totally tear the city up. Let's focus on what's important, okay?
Then once Sauron is defeated, Gandalf has to point out to them that the King has returned. Only the King could have wielded the sword and enlisted the help of The Grateful Dead, and didn't Bilbo point out to everyone way back in Rivendell that Aragorn was "the Dunedain" -- the Man of the West? It was right in front of us the whole time, and JRRT kept adding more and more clues throughout the story, and most people still didn't figure it out. Even naming the third volume "The Return of the King" -- which just might have hinted that that was an important event -- wasn't enough. Most people just wondered what in the heck that had to do with Sauron and The Ring and all.
I'm thinking that's either some seriously good writing or seriously bad writing, and it ain't bad.