Sounds become annoying with time. But visual cues are often automated and ignored. This is why the current solution works best.

Because of the way we evolved, a sound automatically makes our brain alert. At first it's ok. But with time we learn that there is no actual danger. And the sound only becomes annoying. Making us alert for nothing.

Visual cues are treated differently. If something is deemed safe or accepted by the brain, you automatically start ignoring it and focus on something else. So an acknowledgement comes only when something is different. And even then, we simply notice it. It's not an actual alert like sound is.

So the idea is bad. It goes against the way our brains work.