Valve has confirmed that Apple has removed its Steam Link iOS application from its App Store. The company removed Valve's application because it deems it to conflict with its guidelines.
According to a recent announcement, Apple has removed the application from its App Store because of "business conflicts with application guidelines". The application was first approved but was revoked and removed not much later.
Because Android is a more open platform the application is still available there. iOS users who wish to use the Steam Link application can purchase an Android device instead.