Oh dear. Seriously; lyrics are not poetry. I had this argument with my wife on Saturday night, and she still doesn't accept it.
But it's true. It doesn't mean that they are any less viable as thoughts or any less valuble. It's just that you can't read song lyrics and expect them to be a poem. And you can't sing a poem and expect a good song.
An obvious counter argument would be Morrison or Dylan. But try it:
Morrison wrote poetry, and he wrote lyrics. But ne'er the twain shall meet. Not to say that he didn't recite poetry over music "as lyrics." But that doesn't count; we're talking true sung lyrics vs. poetry.
Dylan writes mainly lyrics, and while they come close, they fall flat as poetry. Try it with Desolation Row, Visions of Johanna, It's Alright Ma or A Hard Rain's a-Gonna Fall. Great words. Horrible poems.
I agree....lyrics are always to a degree restrained by the music. With poetry I guess you have total freedom to express yourself purely through words regardless of form, rhyme or whatever. Lyrics rely on the music to enhance the emotion, and in turn the passion of the music is enhanced by the lyrical subject & style. Of course some lyrics verge on poetry when you read them alone, but most times you can tell that they have been written with the music in mind.
In music the melody & song will always be the most accesible part. Although lyrics are important, the music is what grabs you first and sucks you in....then after you loose yourself in the sounds & textures of the song you start to listen to the words, and it's like the music carries the words along in your mind, but with poetry it's less passive and requires more effort and imagination.