The Lord of the Rings doesn’t end with Sam returning home. Tolkien provided detailed timelines and backstory to explain what happened in the years following the War of the Ring, and also the years proceeding it. If you followed along with the timelines and events, you realize there was a whole bunch of stuff happening at the same time as The Hobbit. Tolkien’s story wasn’t confined to the main chapters of his books.
Sure, there are the “CliffsNotes” crowd who only want the basics of the story. Just a summary of what happened so they could pass themselves off in a reasonable fashion in internet arguments, but with stories as good as The Hobbit and The Lord of the Rings you’d want to know the whole tale. Every bit that Tolkien wrote about the characters.
I’ve seen people complain that The Hobbit should’ve been one 45 minute movie or some other crazy bit of hyperbole. If they want a one-movie, “CliffsNotes” version, of The Hobbit…that still exists with the Rankin/Bass animated version. But as Peter Jackson had the film rights to the entirety of the text of both The Hobbit and The Lord of the Rings, he was able to access the Appendices that Tolkien wrote, which explain a lot of stuff that happened at the same time as The Hobbit. And that’s why I love this trilogy.
Sure, there are some things that will always bug me. The entire High Fells bit makes me cringe (the Witch King never died, and wasn’t buried), but the other stuff from the Appendices they filmed I love. I’ve seen a lot of people bitch about the Dol Guldur stuff, but that’s an event that’s not only detailed in the Appendices, but in the text of The Lord of the Rings itself (specifically in the Council of Elrond chapter). Filming stuff from the Appendices doesn’t just tie The Hobbit to The Lord of the Rings, it also makes all six movies a more complete telling of Tolkien’s Middle-Earth.
And The Hobbit wasn’t the first time Jackson and crew pulled from the Appendices, they were doing it in The Lord of the Rings as well…but I don’t see anyone bashing that trilogy for doing so.