Because more people will complain about no sound than too loud sound. 100% probably means "as stored or received" l. Most sounds provided will be adjusted to b

Because more people will complain about no sound than too loud sound. 100% probably means "as stored or received" l. Most sounds provided will be adjusted to be somewhat inside the ceiling before you get distortion. But perceived volume is dependent on many things like frequency. And audio compression, where volume peaks are lowered to allow the whole thing to be made louder is often used for ads, so they sound much louder.