Take for instance a Webbrowser. You could implement one using ncurses, etc. like links, lynx, etc. But for the screen reader this is just a terminal window with a bunch of text.

A Gui can help the screen reader to know which part to read when and how it releats to other parts of the GUI.

Also as a blind person, you live in a world of people that see. You cannot expect every developer to take care and cater to your needs. A GUI that takes care about this automatically for the developer means the dev can just continue doing their thing. While the blind people, can benefit from it as well.

1. Disabled person not the one who controls what gets run.

2. Disabled person not the one who controls what is installed on device.

3. Joint use by two people of the same app.

4. Disabled person wants to be able to ask someone for help who can interact with the app "fully".

Take features like voice control for example where a motion impaired person can still enjoy visually rich content. https://youtu.be/aqoXFCCTfm4