The focus on clarity of thought is a modern shift, or at least the "modern preference". Hemingway was a big proponent on short, direct sentences and few or no adjectives.

In the 1800s and early 1900s, complex sentence structure signaled intelligence for both the author and reader. It was a form of entertainment, in a way, when books were few and nights were long. Try reading Henry James for an idea about what this looked like in practice. Shakespeare is another obvious example of "heightened language" besides archaic words the play are written in iambic pentameter and the spoken text is far from natural (yet incredibly precise).