Sounds like bad design though. It's normal for embedded devices to have a non upgradable bootloader that can always be triggered at boot and is able to reflash a pristine copy of the original firmware wiping whatever was later written. iOS does that (see DFU mode), and all embedded devices I design at work do the same. Why an Android device shouldn't? Apple devices are nominally warranty voided when you jailbreak them, but since you can always reflash an original firmware leaving no traces behind, it's basically moot.

NOTE: no sarcasm here, I'm genuinely interested on why android phones can be software bricked and can't have a boot loader like anything else.

Android devices have similar failsafes (e.g. recovery, fastboot mode), but since they're part of the infrastructure that validates that you're only flashing authorized changes, you are often working around them when you modify your device.

Which is exactly the problem, the fact that you have to work around them to begin with.

Which means that the barrier placed by Android manufacturers is artificial.