Because The Queen doesn't talk to the media, never has, and probably never will. Her Majesty has learned from others that absolutely anything she says or does is scrutinised, and often twisted to mean something to suit the media spin of the day. In order to minimise that situation, she ensures that all comments are through her official Palace spokesmen, and are carefully thought out, and utterly neutral. Interviews are usually given by people who want to publicise something, or make a particular point. The Queen has no need for the former, and apparently no desire for the latter.