Don't forget Tolkien is from an era where there were no word processors for editing on the fly. If you want to change a word on a page from a typewriter you can type the whole page out again (ignoring what indents that creates for the rest of the chapter).
As a wannabe writer I would not even have bothered trying without all the tools we have to hand now.
Tolkien was also inventing a lot of this stuff rather than basing it on or taking inspiration from the body of fantasy literature that he inspired, plus it was not intended to be such a sprawling epic when first conceived. So the final product does feel like it's dwelling way too long in the Shire and on tangential stuff like Bombadil. I have cut my first chapter to death (the only part of my book I originally envisioned before it expanded into something much longer) over years as certain characters need to be there for future chapters to make sense. On old school technology, even with a monster idea I would have just said F it when it came to mega edits that completely change early chapters.