Which it is. Apple has been praised for the accessibility of both macOS and iOS for years if not decades, accessibility concerns have been baked into Cocoa forever. And accessibility is literally a top level category of the Settings app.
And I know that Windows has been improving by leaps and bounds.
> The OS can, for example, run OCR on the entire screen and turn bitmaps into selectable text, read text out loud, etc
That exists (look up VoiceOver Recognition). However it can not be reliable, and will never be anywhere near as good as actual semantic annotation.
Image recognition has no way to understand that the physical UI layout has no relation to its logical setup, nor does it have any way to differentiate between semantic and decorative content, or to see through invisibility to know that a button is a menu versus an action.
Usually it means that you need a deferred mode semantic tree of the application for accessibility UI to walk through, though.