So, at the beginning, Linux started with console only for us blind folks. It is only in 2007 or so that the GUI really started taking off. Back in the days of gnome 2, the accessibility was extremely impressive. The UI was fluid, and every program in ubuntu (that's what I was using back then) was seemingly designed with accessibility in mind. Reality was probably different, but to me, it seemed this way. I loved it. Ubuntu 8.10 was the first Linux I ever used. Of course, QT was not even on the table yet when it came to accessibility, but, it was the glorious days of GTK.
But then, you may be wondering, why did it change? There are probably a lot of reasons why that is, but I can think of a couple.
One, technology keeps on evolving. When GTK 3 got introduced, it took quite some time for the single GUI screen reader to catch up with it. Regressions were also a thing. Not to mention that the orca screen reader has only one really active developer.