On mobile it makes sense, since the user has much more direct control over the scrollable area and the area is quite small. The thing is, apple has been trying

On mobile it makes sense, since the user has much more direct control over the scrollable area and the area is quite small. The thing is, apple has been trying to converge the desktop and mobile UI into one single interface, and this is a prime example where this approach fails. A visible scrollbar is extremely important to the desktop user, but not really so to the mobile one.