Lord of the Rings, as a novel, is inherently darker and more adult than The Hobbit, which was meant to be a children's tale, more or less. The designs of the films reflect this: LOTR had a more dreamy, spooky, dramatic style, whereas The Hobbit had a more bubbly, bright, and accessible style. Also worth noting is how modern cinema convention (48p, 3D, digital) coincides with the stylistic aims of The Hobbit, so PJ got the funding and ran with it.
It sounds like we fall into similar camps about film: we do not have a preference for hyper-clarity because we feel that too much photo detail can ruin the magic. Hence my hatred for 48p, 3D, and most digital films.