A head of state is always a bit of a pain to interview. Technically speaking that is, particularly if there are TV cameras involved. There's always the strict protocol involved, which is more often than not on the excessive side, especially if the protocol staff enjoy their little power and jump at every opportunity to wield it. To be sure a leader of a country has a full agenda and every second of his or her time is precious and cannot be wasted on little things such as answering questions from the media.

Often questions have to be submitted and reviewed before hand, just in case there are topics that are out of bounds, and there is a question of language. In my experience, even if the president or prime minister speaks English fluently, protocol demands that they speak in their vernacular, presumably so the official translator could gloss over errors in data or information and the head of state sticks to the scripted answers - hence the need for the list of questions in advance.