How about many of those OS-level restrictions can be bypassed by hacking into private APIs, which is one of the things that'll get you banned from the App Store

How about many of those OS-level restrictions can be bypassed by hacking into private APIs, which is one of the things that'll get you banned from the App Store? The OS does what it can, but the OS is entirely out in the open to be hacked, bypassed, subverted, worked around and so on. A pair of human eyes and a private app scanning process does what the OS can't. No, it's not perfect. It's not even great lately. But it'd be worse without it, as you can witness on desktop operating systems.