Accessibility is more than just screen readers. Toasts are also not accessible for folks with low vision, low peripheral vision, etc. And the time-based disappearance is unpleasant for many people, as one of many examples of "accessibility improvements are also often usability improvements".

A message that you have to explicitly dismiss, and that's stored in a "message history" somewhere, is much more accessible and usable.

There's no such thing as accessibility. Accessibility is just usability.

Toasts have poor usability because its easy to miss them. This makes them bad for everyone, regardless of screen reader.