These two things are linked in my opinion.
Tolkien created a world and didn't have anything to do with it, so he wrote
The Hobbit and
Lord of the Rings. It's a miracle that Tolkien put all his world building to good use.
Wait, did I say "all", I met most.
I think Tolkien created Tom Bombadil but didn't know what to do with him. There is nothing wrong with Tom Bombadil as a character but he doesn't advance the Lord of the Ring story in any way. At least as far as I can see, and other Tolkien fans agree with me. Though if you disagree, I don't think you are a bad person.
Let's talk about Rowling and George R. Martin.
Rowling has characters she created and liked that she cut out of early drafts because they didn't advance the story.
I couldn't finish book 4 of
Song of Ice and Fire. I would argue that each book was less good than the last. Because George R. Martin keeps adding extraneous details.
I'm a guy who loves making extraneous details. I have a massive website feeding
my obsession for extraneous details but when I write a story I try to keep the details lean.