Poetry is a profoundly conservative use of language. It conserves not only values and ideas but the very language itself, so that even some grammatical forms that ought to have disappeared long ago are still around and useful for special effects. Prose is progressive and disruptive. It must subvert or elude the poetic qualities of speech to go about the business of logic and analysis. Discursive prose is essentially antisocial, subject to constraints and regulations that would be unsuitable, perhaps even rude, in speech.
Writing is an audacious and insolent act.
When we write, we call the other members of our tribe to order. We command their attention. We assert that what we have to say is valuable enough that they should give over their idle chitchat about the weather. It had better be. The mere appearance of discursive prose promises those things.