Correct. Its locked down so that it cant be tampered with. Friends, family, thieves, police, three letter government agencies, and even Apple are unable to tamper with it once the user has set up the phone. It is designed to protect your data from anyone else but yourself.

You want to take away that feature from me because you want to load another OS on it? Just go buy a Pixel phone and flash GrapheneOS on it.

There are sooooo many devices out there that do not have any way to unlock bootloaders. Why are you focusing so much on Apple and their secure bootloader?