The fundamental problem is that someone somewhere decided that setting up signing keys was too hard, and that because of this the manufacturer should be in char

The fundamental problem is that someone somewhere decided that setting up signing keys was too hard, and that because of this the manufacturer should be in charge of setting up the keys. so now instead of you owning your hardware and setting up the keys on first boot, Microsoft owns your hardware and the keys are theirs. And in a case of self fulfilling prophecy, because they decided that initializing and owning your own keys was not going to be a normal part of the user experience, it is now hard(almost impossible) to do. If instead the decision had been made to have the user set up some keys and authorize the OS, the process would have to be streamlined and easy. In conclusion, signing your operating system is too hard, unless you are in the happy path where your OS is signed by Microsoft it is far easier to just disable the infernal subsystem as it gets in the way.