* They have a CONSISTENT user interface. I am emphasizing this in caps despite going against style guidelines here because this is such an important thing that has gone out of style outside Apple. Everything in MacOS and iOS look and behave the same. Users worship consistency.
* They know and respect how humans behave. Ever seen those Windows desktops filled to the brim with icons? Well that's how most users use computers, and so that's how iOS presents itself to its users: All the icons on the screen, scrolling probably necessary but they're all on the screen.
* Following on the above, they know and respect that humans abhor complexity. Apple's mice have one/zero buttons because I can't tell you how many users simply do not understand nor care about left- and right-clicks, let alone middle-clicking the scroll wheel. Apple knows and respects that.
TL;DR: Apple is top dog because Apple is the only computing company that knows how to human.