Are there any things that don't traditionally make noise that we should also add noise to? Sharp drops near pedestrian areas? Bicycles? Low hanging branches over walkways?
Bycicles have bells. On shared paths, pedestrians don't hear cyclists coming from behind, so you occasionally give them a ping.
Note that I'm not advocating for adding noise to these things. I'm just trying to point out that there's a status-quo bias where we're willing to retain unnecessary noise but not to create it.
You only sound a horn if the driver thinks it is needed, whereas pedestrians & other vulnerable road users are making all sorts of judgements using audio clues that the drivers are completely unaware of.