As trisher says, the point being made is that people in influential senior positions, such as those in the media, law, politics etc., have a huge amount of power over other people's lives.
Obtaining, for instance, a trade apprenticeship does not confer such power or influence. Builders, plumbers, electricians, etc., do not decide which stories are going to be covered in the newspapers or on the TV news, and how they will be presented. They do not decide which potentially controversial documentary or exposé brought to them by independent film makers will be accepted for broadcast. If the people responsible for these sorts of decisions come primarily from a very narrow range of society, there is a real possibility that the decisions they make are influenced by their own experience, views and values and do not reflect wider society.