Are they really? Isn't it pretty normal "role status aria something something polite" thingy to announce feedback to user?
A message that you have to explicitly dismiss, and that's stored in a "message history" somewhere, is much more accessible and usable.
To make this a little more concrete with one example: if you are using fullscreen magnification, odds are toasts will literally never appear on your monitor. By the time you pan over to their little corner of the screen (if you ever do), the toast will be long gone.
a "big banner image", buttons that are required to interact or dismiss, doesn't go away on its own after only a couple seconds, and might(?) also exist in the notification center
I think it's pretty safe to label that "definitely not a toast". That's just a notification, or maybe a "non-modal alert". Toasts are distinct from those by being brief and ephemeral.
Toasts have poor usability because its easy to miss them. This makes them bad for everyone, regardless of screen reader.
