The great enemy of clear language is insincerity. When there is a gap between one's real and one's declared aims one turns as it were instinctively to long words and exhausted idioms like a cuttlefish squirting out ink.
Poetry is the language we speak in the most terrifying or ecstatic passages of our lives. But the very word poetry scares people. They think of their grade school teachers reciting 'Hiawatha' and they groan.