Partly because they document the doors which are there for LE : https://www.apple.com/legal/privacy/law-enforcement-guidelines-us.pdf https://www.apple.com/lega

Partly because they document the doors which are there for LE : https://www.apple.com/legal/privacy/law-enforcement-guidelines-us.pdf https://www.apple.com/legal/privacy/law-enforcement-guidelin... They also switched a few years back to provide signed firmwares rather than encrypted firmwares to ease independent verification, and have the Apple Security Research Device program to do runtime exploration with certain security walls turned off. (Supposedly creating these devices requires a partial factory retooling) Apple also only has per-device global builds, rather than regional builds which might obscure requested features. My understanding is that they take transparency measures to make sure it can be detected if a firmware was released out-of-stream, and anonymity measures to prevent targeting a specific device with a custom firmware. The Secure Enclave also requires the device passcode as part of an approval process for installing new device/enclave firmware; the underlying OS and security enclave are not meant to have the capability of being transparently updated/modified.