It does actually perform a security function. The lid angle sensor is used to know when the device is open or closed, and when closed, it physically disconnects the microphone. If you were to be able to recalibrate it at any time, you would leave your device vulnerable to having the microphone enabled when the lid is closed. You can argue whether that justifies the practice, but it's not as simple as just burning the EEPROM serial number in that tells it to turn the display on or off. It defends the user against an attack vector.

From that perspective making it one-time programmable is not unreasonable.