Kwaito doesn't stand alone though.
Note how hip hop has become less and less about issues, and more and more about who has the most nut-hugging jeans and silly dance steps, while those artists who still try to make music with a message, are shunned at home and enjoy cult following overseas. This indicates that something in what they are saying doesn't sit well with the powers that be and its in their interest to keep them in the shadows, rahter than having them get the same exposure as say a JR or Jozi.
There are a few exceptions, like Tumi and the V, but I think this may have something to do with him being less militant and in your face with a f*** you.