Parliamentary Voting System and Constituencies Bill

As my right hon. Friend knows, I am a new Member. When I arrived, I was surprised to learn that we already use the alternative vote system in the House. Mr Speaker was elected through that system, as are the Chairmen of Select Committees and the members of constituency Labour parties, and as the new leader of the Labour party will be. If they can have that system, why cannot the good people of this country have it in order to elect Members of the House?