Focus of the performance is the music itself. A large part of the art form's appeal is it's visual impact 2. Most of the appeal is the music's aural impact. Patrons attend to hear an orchestra. Players move from one place to another around the audience, allowing audience members to experience different mixes of the arrangements.
Musicians remain stationary on stage.
Music is memorized. Music is read off of a stand. Communication between musicians and audience members is important. No communication is necessary between musicians and audience. Leader faces audience.