They need their own voice, and a custom typeface gives them just that. Apple is famous for being a leader in design, so something just doesn’t sit right with them using the world’s most popular font across all of their devices. This is why you’ll see it on signs in airports and subways the world over.
Helvetica Neue (and the original Helvetica) are known for being a bit “stale.” They’re generally used when you don’t want the letters to get in the way of the information. Helvetica Neue was designed in 1983, and pixels weren’t a consideration back then. Screens are made up of pixels, and, as you can learn from Garamond, pixels aren’t typography’s best friend.
Visual Design Course | White Space Course San Francisco Font: Apple improved on a classic.