What about Notepad++ makes it work with screen readers while Sublime and Atom don't?
..., Notepad++ is written in C++ and uses pure Win32 API and STL which ensures a higher execution speed and smaller program size.
And which lets it piggy-back on Windows' accessibility features, which seem to be quite good.
I guess Sublime Text and Atom draw their own GUIs to get more control over the look-and-feel, but don't add the necessary hints to make screen readers work.