I'm sure you meant this with your post but didn't specify it - of course there are songs that aren't poetry as well. But good song lyrics are poetry. I raise this mostly because I had a working theory for a while that most if not all songs could be poetry and it would be possible to effectively "compress" any song into a poem - one of the biggest differences that potentially makes lyrics not-poetry is their reliance on repetition - by removing repeated phrases that are clearly present in the song to make the lyrics fit the rhythm. It was an interesting theory but I put it to the ultimate test - Blurred Lines - and I'm sorry, after a deep dive into those lyrics I don't think there's any way it can be called "poetry." No matter how many repeated lines you pull out.