OT, but his style is so dense in that book. Why did he write it like that? I've never been able to finish it. I find it almost impenetrable. The Hobbit I read with joy and ease even as a young child. In LOTR, sometimes after reading a paragraph I needed to pause to digest and to connect the dots. In The Silmarillion I need that pause after each clause.
This sucks, because I _need_ to know what's in the book.
I think two key points as to your question of _why_ he wrote it like that. First, it is not a novel that he planned out and then sat down and wrote. It's an amalgamation of disparate stories that Christopher cobbled together into a single book because that was the only way they could sell it to the publishers. It's also the quasi-religious tome of the Tolkien world, so rather than comparing the readability to a Stephen King novel, compare it to something like the Bible or the Torah.
All that said, it took me several reads before I felt like I really 'got' it. The hardest part for me was grasping the long timelines since most of it is a story of the elves and they are immortal. You might be following the same character arc for thousands of years. All that struggle was worth it though, because when you reread LOTR _after_ reading The Silmarillion, you pick out things in LOTR that you didn't even know were there before.
Afaik The Silmarillion was more of a backstory, not really fit for publishing at Tolkiens death. Christopher was the one I believe who collected all the materials into its current form. Don’t forget Tolkien himself was a master linguist!
Checkout this talk by Brandon Rhodes - it explains the context in which the Hobbit and LoTR were written in. I won’t spoil it, but I think it’ll answer your question.
This sucks, because I _need_ to know what's in the book.