Why do you see Beck on O'Reilly, but you never see Hannity on O'Reilly or either O'Reilly or Beck on Hannity?

Does Hannity just not get along with the other shows or something? He's a team player towards the people he lets on his show. He needs to get out more. Not because I'm a fan of any of the three, but it would jazz things up and I don't see why he doesn't considering he has the same views.