There was an article about iOS security where someone argued that Apple controls the enclave for security reasons, to which I answered that this is basically security by obscurity. You can see I was downvoted for this: https://news.ycombinator.com/item?id=13676135

I still downvoted izacus because it was an uncharitable fanboy rambling. The charitable interpretation would be that the walled garden (in regards to the enclave) is a side effect of their implementation, and not the intention.