it comes from the fact the divison is seen as very weak and the bros are at the top, theres never been two brothers at the top of the heavyweight divison and they aren't goner fight eachother so they use there power to put in the contract that clause....untill someone comes in a knocks them off they'll have there way lol. funny how other fighters will bow down and taht the fights but our so called saviour david haye somehow can't sign and carry out a contract with them