Well akshually.... the bootloader is initially not unlockable. You must connect the phone to the internet. Within a few minutes a background process will reach out to Google servers to check whether it was purchased outright or with a payment plan. It will only enable the bootloader unlocking toggle after this step. Phones bought with a carrier contract won't be unlockable until paid off.

In those initial few minutes (/ before you connect it to the interwebs), the bootloader unlock option in the developer settings & fastboot will be disabled.