It may well be that Apple is special, but in general, large software companies are motivated to care about accessibility primarily by the prospect of lucrative government contracts, for which there are usually mandated (by law) accessibility requirements. The problem for smaller companies is that accessibility doesn't scale down well - you need a lot of upfront investment (education, processes, testing etc) to get anywhere at all at first, but then all that remains useful for many more projects to come.
I read somewhere that screen readers look for a flashing vertical line, to detect the caret position in systems that don't expose it via the OS's APIs. I can't find a reference for that right now, though.
https://en.wikipedia.org/wiki/Microsoft_Active_Accessibility
It may well be that Apple is special, but in general, large software companies are motivated to care about accessibility primarily by the prospect of lucrative government contracts, for which there are usually mandated (by law) accessibility requirements. The problem for smaller companies is that accessibility doesn't scale down well - you need a lot of upfront investment (education, processes, testing etc) to get anywhere at all at first, but then all that remains useful for many more projects to come.