Why do poets use anastrophe in their writing? Who else besides poets use anastrophe?
It can evoke other times and cultures; other times, it just facilitates a rhyme.
Anastrophe is the reversal of word order in a sentence, usually a noun and an adjective. Sometimes, this is done to evoke older speech patterns and convey a sense of antiquity ("The body politic," for example). A lot of wording in the King James Bible is in a different order than a modern English speaker would use, and mimicking its tone conveys a sense of importance and depth.
Also, other languages use a different word order than English. Mother's Day in Spanish is "Dia de la Madre," Day of the Mother. Saying the words in this order gives the idea a dash of old world glamour and exoticism.
German and Yiddish put subordinate clauses in front of their main sentences and sometimes move the predicate verb to the end. Borscht Belt (Jewish) comedians sometimes use this pattern in their jokes and storytelling to evoke life in the old world, or the old neighborhood, "For this, I gave up my weekly schvitz?"
Poets and songwriters use anastrophe for these reasons, and for one other: Changing the word order helps set up a rhyme in another line. "Once upon a midnight dreary, while I pondered weak and weary..." (Poe, "The Raven")