40's style is not immediately catchy.
Yung Joc, Yung Jeezy, DFM, Yung Faggot and all the other assorted studio gangstas make music that is catchy on the first listen.
40's music, in fact 90% of the hyphy music that they are trying to commercialize, is not. People don't understand the 22+ slang words that will never be used outside the bay, they can't get into Keak's lyrics that no one can understand, and 40 has not made a single that will blow.
The people have spoken, and 40, Keak, and other's presentation, song choice, and way they have been representing the bay failed, straight up. The downhill slide has already been going for a few.