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.
Conductor faces orchestra, his back to audience. The show is only part of what the audience is there for. People are only there for the orchestra concert. The audience sits quietly and listens to the performance. Care is taken in arrangements to see that each voice contains movement at all times.