Which is why most systems that allow you to change the boot chain or otherwise mutate the chain of trust will clear the storage on the device (such as unlocking the bootloader in Android). And on Chromebooks, you cannot easily (read: without getting a flash programmer and doing it manually) subvert the boot chain and not let the user be aware of it (that's what developer mode is used for -- it shows a scary warning if the measurement and secure boot are disabled).

The reason nobody mentions this is because the solution is so trivial there's really no point in repeating it each time.