Why are mumble rappers not cool

Rappers labelled as "mumble rappers" also tend to use the "aye" flow, where they add words such as "yeah", "aye" and "uh" to the start or end of their lines. "Mumble rap" is often used as a derogatory term in reference to a perceived incoherence of the artist's lyrics.

because they mumble

Explanation:

like there also just dont say clear words