Comment by surajrmal

Right, because the android security model considers app developers independent entities with security privileges equal to those of the device owner (in that both parties need to authorize access for things to work, the device owner doesn't have more privileges than the application developer when it comes to the application). Those mechanisms are necessary for that security model to work. If you want to operate with a different security model that's fine, but you just need to use something other than Android. The bootloader situation being optional is Google not getting overly involved in the device maker's business outside of the scope they should have influence on. And they set the precedent via Pixel for how they think others should do it.