How do you know it doesn't? If you consider the possibility that QM plays a role in the conscious process, then it wouldn't be only the brain that shapes the consciousness. It is still very early in the development of a working model regarding QM decision-making. Much more needs to be done.
All brains, chickens, mice, rats, dogs, cats, birds, crocodiles, etc, etc, etc, have the same underlying quantum substrata, yet the behaviour, thoughts, perceptions of the world, and so on, is specific to the brains of species and to some extent specific to the brain of each individual member of a species...according to its personal experiences encoded as memory.
Now where do you see QM as a factor in relation to doing something that the architecture of a brain doesn't do?
Can a mouse learn calculus? Can horse learn to speak Mandarin? Can a cat learn to read music and play piano?