because it an iphone, which is very closed. everybody know apple doesn't allow the developers to do a lot of things, like multi tasting etc, and that they are very strict with their developers. From what I remember even the cpu is undercloacked and doesn't run at it's full potential, because it will eat their battery alive. apple will never let a developer use what ever he closed.
and lets not count jailbreak since from apples point of view that's illegal