It's not just rap, though - song lyrics have been poetry, for a long time now.
Time Ticking away the moments that make up a dull day
You fritter and waste the hours in an offhand way.
Kicking around on a piece of ground in your home town
Waiting for someone or something to show you the way.
Tired of lying in the sunshine staying home to watch the rain.
You are young and life is long and there is time to kill today.
And then one day you find ten years have got behind you.
No one told you when to run, you missed the starting gun.
So you run and you run to catch up with the sun but it's sinking
Racing around to come up behind you again.
The sun is the same in a relative way but you're older,
Shorter of breath and one day closer to death.
Every year is getting shorter never seem to find the time.
Plans that either come to naught or half a page of scribbled lines
Hanging on in quiet desperation is the English way
The time is gone, the song is over,
Thought I'd something more to say.
Home
Home again
I like to be here
When I can
When I come home
Cold and tired
It's good to warm my bones
Beside the fire
Far away
Across the field
Tolling on the iron bell
Calls the faithful to their knees
To hear the softly spoken magic spell
Hard to read it without hearing the music, right? I made a similar comment about another set of lyrics a while back, here : https://hubski.com/pub?id=30950
(By the way mk - hubski search still sucks (sorry!), I couldn't find this old thing until I asked google for it).
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.