It's over because they lost viewers this season (that equals money), Iyanla wasn't going to come back, and I speak for myself when I say that if I had had to watch one more season of Rhonda's smarmy grin and punishing her hg's - I wouldn't have watched.Money talks and SO wasn't bringing in the money anymore.
BTW - there is a ton of discussion on this very topic in this thread -
http://community.realitytvworld.com/boards/DCForumID91/1122.shtml