Why though?
Sharks are attracted to sound
I thought this but when that's introduced as a 'theme' in Jaws 2, Brody acts like it's entirely new information to him.
Then it was to avoid panic stampedes.
I thought it was blood
are they though? or is that just the thought that your mind kind of assumes when you hear that line in the movie ?
My take has always been to keep from spreading panic.