I think the lack of progress can be down to disabled people not being the target demographic of Apple. Apple shiny’s are a lifestyle statement. “Look at me, everything is beautiful, and so am I and my Apple, were perfect!”.
To develop tools for the disabled is a passive admission that not everyone is perfect, and that some people need additional functionality to perform tasks. Apple on the other hand like to brag how they specialise in reducing tasks to a minimum compared to other platforms, they use it as a selling point.
If they start to offer additional functionality for disabled users, and it works, then you can bet that it will work just as well for the non-disabled and they will start to use it. Then suddenly apples minimalistuc UI is no longer it’s selling point. Better to do nothing and hope disabled customers go somewhere else and stop making the brand appear ugly.
Me cynical? I’ve found that with Apple I’ve never managed to run out of it. The cynicism just keeps flowing.