They all keep their mouths shut because of a non-disclosure agreement - but things still leak out through "reliable sources." Everyone used to be terrified of "brave kind Phil," who could finish their careers in a flash if they upset him. However, the times they are a-changin'. Too many people know he's not what he seems now and his popularity is on the wane (he didn't even make the shortlist for "Best Presenter" at the NTAs for example) and as he becomes less loved, neither does he have the clout he used to have. And as he loses his power and control over people, all his "secrets" suddenly don't seem so safe anymore.
It's only a matter of time, you wait and see!