because he is a top producer in a stale climate which doesn't have too many producers that could make hits right now, plus the same shyt gets played on the radio all the time.
compare that to lil jon who was on top when the Neptunes, just blaze, kanye, manny fresh, david banner, paul and juicy j, cool and dre, Scott storch, ect who was all huge producers at the time he had to compete with.
if mustard last another 2-3 years then you can compare him to lil jon, dude will be lucky to make it to next summer