Why is Apple's iOS 16 on/off sound exclusive to the iPhone 14 / Pro series?

Apple's latest addition to the new iPhone 14/Pro lineup adds a new accessibility feature that allows the new phones to play a sound on boot and off, similar to the iconic Mac boot sound, which can be turned on or off in the settings of iOS 16.

However, the switch-on sound is exclusive to Apple's iPhone 14 / Pro series, and is not available on other older iPhone models that have been upgraded to iOS 16. According to 9To5Mac, this limitation is due to the fact that the on/off sound is not part of the operating system.

When the iPhone displays the Apple logo, the phone is in the bootloader bootrom stage, and the bootloader sound is built into the bootloader and embedded in the A16 / A15 bionic firmware, and the bootloader bootrom is read-only and cannot be modified afterwards. As a result, Apple is unable to add this switch sound to older iPhone models prior to the iPhone 14 / Pro series.

Apple iPhone 14 / Pro Series users can manage on/off sound under Accessibility in the Settings app. Note that the iOS 16.1 beta version seems to have a bug that prevents the switch-on sound from playing.