Because that challenger is still the draw. When Oscar lost to mosley, Oscar still got the majority split for a rematch offered as he was still the money man. The split would be better for the new champion but 50% is fair. Rahman v Lewis 2. Rahman got $10 million Lewis got $11 million. Let's not try and make out like AJ requesting at least 50/50 at worse in a rematch is unusual as it's not.