This is a difficult question to answer, since modern neuroscience lacks a comprehensive understanding of precisely what consciousness is and how it is produced.
Researchers haven’t actually identified, as-of-yet a neural correlate in the brain which generates the subconscious processes that lead to the contents or experience of consciousness. That’s the so-called “hard problem”: precisely what leads a lump of grey matter and neural networks to experience a rich inner, first-person perspective of qualia and the reason why natural selection would result in the universe becoming aware of itself in the form of localized, complex chemical beings.
Natural selection could have made equally effective use of unconscious zombies without the “experience” of awareness and just directed by our unconscious/subconscious processes. As such, the reason why the experience of consciousness arose is a great problem for science and remains unsolved, with no theory yet found which one could characterize as the “silver-bullet” that would result in a Nobel Prize being awarded.
So to be quite frank with you, there is no testable answer at present and anything anybody offers in this thread is speculative from a scientific perspective.
I readily admit that I myself have no clue.