I'd have to argue with you on that one... Peter Jackson has always said he makes his movies for himself, and if a wide audience likes it too, cool. His tone in LOTR was fairly dark, and it worked pretty well, but it doesn't work so well with The Hobbit. Some things he got really right in ways only a true fanboy could, like casting Arthur Dent as Bilbo, but others... well I think "story for a younger audience" let loose his inner 13-year old fanboy all over it.
I don't doubt at all that Jackson is a huge fanboy who has put a lot of thought and work into his adaptions. Sure, I would have made some different choices, as everyone else who loved the books probably has something they would have liked to be different. But adapting a story into another medium is tricky (especially stretching the Hobbit into 3 movies), so I'm overall pretty happy with the results.
It's clear however that these movies are aimed at a broad audience, who hasn't read the books, and is completely unfamiliar with the world. That makes sense too because at that budget the studio will want to see a lot of money. It's not "lowest common denominator", but the movies are made to work well for an audience who's just watching for the spectacle.
With potential Silmarillion movies you'd have the problem that there are no hobbits, sometimes even no humans, in these stories, so the audience lacks someone relatable who explores the world with them. There is no humour really, which had a big part in the Hobbit and LOTR (both books and movies). And the stories are pretty dark, evil is never really defeated, everyone tends to die at the end of their story, Children of Hurin even has incest. The most filmable stories are much more straightforward storytelling than LOTR, but they are classic tragedys, they would not work as family movies and they would lack most of what made the LOTR movies so accessible for non-fans. So from a commercial point of view, I doubt a studio would sink as much money into the Silmarillion as they have with the other movies.