It seems to me that Nolan was very deliberately going for colorblind casting (and choosing good actors). It’s enough to say that the script wasn’t very good and the secondary characters are thin!
Idk if Nolan is a Travis Scott fan himself or if his kids are, but it’s sweet he got to cast him and imo he’s pretty obviously trying to place rap music in the lineage of storytelling that includes the poem and the movie itself.
(Also v funny that Nolan got a songwriting credit on the Scott track)
Travis Scott also did the end credits song for Nolan's film Tenet, which was released in 2020. I assume that collab went well in Nolan's mind if he decided to bring Scott back in an even greater capacity this time.