What was bad about arc4random?
There's also no direct equivalent to arc4random() in the new API - you always have to pass a range, which discourages people from using % to reduce the range and introduce modulo bias.
I think that’s a weak argument. arc4random’s source code isn’t platform specific, complex or large and is available under a permissive license, so they could easily put it in the runtime.
I would think they added this because of the modulo argument you give and to give it a better name (there’s nothing wrong with ‘arc4random’ for _a_ random number generator, but _the_ random number generator on a platform should have a simpler name)