I think it's a matter of speed of light vs. speed of sound. Everyone takes their mental clock signal from being able to see the conductor. The conductor, at the

I think it's a matter of speed of light vs. speed of sound. Everyone takes their mental clock signal from being able to see the conductor. The conductor, at the same time, is positioned so that what s/he hear is close to what the audience will hear, which is very different than what each musician will hear. At minimum, the conductor is a clock and a feedback mechanism.