Comment by mehrdada

(not the GP) I think you are attacking the strawman here, as your own post admits, by interpreting "corporate" as exclusively "marketing" and not including technical folks in it. I agree with you the decision is also partially driven by technical folks at the company, but given macOS on ARM is really closer to iOS, the natural course of action would have been to simply clone the iOS model of secure boot, not to rethink it. That observation alone almost certainly implies it has been given explicit thought at relatively senior levels of the engineering hierarchy, at the very least.

My take is the company deliberated about this trade-off quite explicitly at some length and decided the Mac serves the world in its current capacity as a "computer" (i.e. the truck in the truck vs car analogy) and that they do not wish to limit the capabilities of the existing Mac that people love in any shape or form by moving to ARM, which was highly speculated and ripe for potential backlash. They probably decided the Mac would be an "open" system to some degree (at least as open as it already was) and iOS would be the closed mass market computing device optimizing for security and dependable end-to-end experience.