it doesnt even have that much to do with is the artist good or bad its more of a sound and vibe thing...It might be hard to wrap your head arounds, or maybe not but most rappers sound like complete ass onstage. Almost none of them have mastered instrumentals so that leads to an uneven transition from set to set, not to mention sound guys DESPISE rap music so they do the bare minimum at these events...
ever been onstage and one minute you hear yourself and the next your mic is super low? Thats cause your druuuuuunk ass hype man is screaming his off beat adlibs way too high and the engineer has not idea whos mic is causing that distortion and he doesnt care so he slides BOTH ur faders down, you are onstage OBVIOUSLY distracted cause you cant hear yourself, the crowd notices, they begin to file one by one to the bar and BAM! The vibe has been lost.
or how about your track drops and its waaaaaay to low cause the artist before you had a polished set cd, you re all amped up to rip it after you heard the previous act sound awesome, then your music comes on sounding thin and whimpy so you start with the "uh, gyea, turn my joint up" but the engineer is turned around distracted, he doesnt adjust ur volume until the end of the first verse....thats a lifetime onstage, all your swagger is lost cause of the sound issue, the crowd notices and hits the bar....vibe lost
theres so many more ways too...nobody goes to a club to see locals perform, except other locals.