Why do live bands sound better with live singers vs. live rappers? Subjective I

Question:

Why do live bands sound better with live singers vs. live rappers? Subjective I know.?

I'm not familiar with musical terms, so this might not come across clearly to some.

When rappers rap with live bands, the sound doesn't seem harmonious, unlike singers with live bands. By harmonious, I'm trying to describe how the rapper's voice doesn't blend in well with the background created by the band. How can you explain it?

Best Answer - Chosen by Asker: The people fronting live bands are singers.

Rap artists are poets with their work set on top of the beat.

Apples and oranges, really.