Hip-hop and rap is music that isn't known for intellectual lyrics or even human decency. If that is used as the basis for your expectations, then being mere average as far as coherence goes can already be considered amazing. If your expectations are based on a normal level though, then "amazing" turns into "average at best".
I hope that explanation helped.
To people who don't know anything about hip hop except trap and gangsta rap, this is probably true. The culture extends far beyond that narrow-minded view however.