We're not sure exactly. Either of the top two answers could be correct.
1) A moving target is harder to hit.
2) To get away from the noise.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
3) So they don’t get mobbed by fans.
(I LOVE bagpipes)
Why do commentators whisper at golf tournaments? They don’t want to wake anybody up....