@jamesthomson I suspect the reason is that those icons began on iOS, where the “save” icon most often means “take this photo [from an app/website/etc.] and keep it in my device” and the “share” icon means “take this item and send it to someone else’s device.” They make sense in that context, less so on MacOS.

I can’t say why they went with the arrows they did for icons that didn’t already exist, but I wouldn’t be shocked if the people who put them there couldn’t either.