I can understand that !@#$%^&*... are useful in their own context. But there are hundreds, if not thousands, of other meaningful symbols, too. Yet, we don't see any key allocated to one of these symbols on PC/Mac keyboards. Why is that?
There are keyboards designed for foreign languages including Russian, Arabic, Japanese, Hebrew, etc. that have keys for the required characters. There are also custom key tops you can buy, stickers for the top and front of keys, flexible plastic overlays, and most OSs have key remapping software.<p>Ages ago, I worked at a very large PC company, and we had a shelf of more than twenty different keyboards we tested with.
Same reason two button mice are standard, it's the balance point between simplicity and capability. An argument could be made for there being a lack of a standard but then I'd expect there to be more keyboards trying to satisfy a market need with extra nonstandard labeling. So the bottom line is a lack of demand.