I think, from his musically techical education Shore is rather a chamber composer. I seem to remember, that in The Fly he had to deal with a full orchestra for the first time and using full orchestra and choir for LOTR was a lot of learning by doing for him. I read or heard it somewhere. And it makes sense to me.
I guess, Peter Jackson and Howard Shore felt connected as both before LOTR had mainly experience in independent horror movies. At least I could imagine that this played a role. Because Shore didn’t have, like Jackson, no experience with productions of the scale of LOTR.