The quality of their software has declined significantly in the past 15 years. That said, it's still pretty good and this is probably down to reducing scope.

Apple's software only runs on their hardware, they regularly exclude recent and capable devices from running the latest versions and they deprecate and ignore insustry standards liberally (OpenGL, Vulkan, Nvidia GPUs). This makes their software much simpler to write. Compare that to Android, which runs on anything, or Windows, which I hear can do crazy stuff like run apps from the 3.X days.