Why wang is not banned since along time ago ?

It is hard to make our posts are voted by the other users. Wang make many post and comments with his bot easily. He take this advantage to get much Steem Power and down it to get STEEM. He doesn't care the upvote but he just collect the STEEM POWER. And he also makes new bot's account named weng for comment wang's post. He has cheated STEEMIT. So why STEEMIT doesn't banned wang's account since a long time ago. Now he has much STEEM that he has transfer to his wallet account outside the STEEMIT.
@pharesim
@ned
@complexring
@blocktrades
@dantheman
@wang
@weng