Consequences of leaving the "walled garden"
Cook is also right in saying that Apple's customers pay for Apple to make choices on their behalf—but some people buy Android devices because they don't want a third party making those decisions.
The "walled garden" can be limiting, but it also ensures a consistent, stable platform.
Apple is unapologetic about its tight control of its platforms. The "walled garden" might seem too restrictive—even draconian—to some, but maintaining strict control of the operating system and how apps interact with it is a fundamental element of ensuring a consistent, quality experience for all users.
Apple is not infallible—just look at the debacle with its Maps app. The flipside of that problem is that Apple knows who to blame, and it has direct control over fixing the situation. Opening up iOS to third-party apps could result in conflicts, crashes, and finger pointing between Apple and third-party developers over the source of the problem.
It can be argued that users should have the freedom to install what they choose, and that they should also understand the potential ramifications and accept responsibility for those decisions. Ultimately, though, problems that arise with third-party apps will reflect poorly on iOS, and have a negative impact on Apple's reputation.
There are customers who want a more open, flexible platform. Apple doesn't need to pander to those customers, though—they can just choose Android.
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