I believe that's because we reserve shouting as a signal during dire situations. It's kind of like the color red, where we give it an inherent dangerous meaning

I believe that's because we reserve shouting as a signal during dire situations. It's kind of like the color red, where we give it an inherent dangerous meaning naturally, but see it enough everyday and your heart will no longer instinctually flutter when exposed to it. Having lived with a person who is hearing impaired, the effects of shouting on reflexive action will dissipate after the first week.