I know exactly what you meant. The problem with your point is Cairns is involved. He knows he is being investigated, many people are pointing the finger in his direction, a lot of the leaked information includes little bits of eveidence which also point towards him. The others you mention have none of that to worry about, which funnily enough, is probably why they aren't defending themselves.....
I do agree that he's probably guilty as sin but in his mind he's decided getting on the front foot is going to be better than waiting for them to come and get him and above all it indicates he will be fighting it until the end.