

It’s a topic I should do more reading on, but the feeling I get is that it was a backlash to the highly progressive currents of the 20s. It affected nearly everything - the Soviet Union had some of the first schools for the blind and deaf, then some of them got shut down. There were women’s work programs, then they got replaced with “traditional family” propaganda. Stalin is undoubtedly the source for some of it, but he was also the head of a huge and popular movement so he can’t be solely blamed.
I looked at my source again and it seems I misremembered - it wasn’t that the progress for the disabled was all reversed, it was that one of the pioneers in the field of special education (I. A. Sokolyansky) was arrested in the Great Purge and his school was shut down, but when he was released in 1940 he was able to go to Moscow and get a new job doing the same thing at a different university so clearly it wasn’t a universal thing.