User notifications on MacOS are definitely standardized, but originally they were Growl notifications until Apple made it a first-party API and iterated on it.
And you are right in that the Growl-style notifications in Mac OS are standard now... but those are different from the ones in question here because they are not related to a control that the user was just manipulating. They could come from anywhere at any time, and thus they must be presented in a location independent of whatever the user is doing.
The Growl-style notifications work well because they're near the top of the screen, too. Users are used to status and information in menu bars and so forth, in accordance with the general top-down convention of presenting information.
Thinking it through, I did actually implement a "toast"-style alert for asynchronous issues in one application. It was at the top of the screen, though. I originally put it in there strictly for debugging, but I think I might have left it in the release. So I'm not entirely opposed to the idea, but mainly its placement in the examples discussed here.
It's pointless pretending there's one perfect guiding philosophy and all others are obviously wrong.