Because if there is no mind and consciousness in the universe and therefore not in any of its parts the question arises as to how mind could possibly manifest in any individual existing element of a totally mindless universe. To say that mind-cosciousness is but a function of 'mindless' material brain structure is also to say there must be a 'reason' external to this mindless brain matter which drives the necessity for this mindless brain to be aware and conscious of its existence and the 'meaning' and 'direction' of this totally 'mindless' universe. Without mind as a universal reality there is no reason for any aspect of existence to be individually conscious. In fact there is no reason for existence, period.
You're just playing with us, right?
Let's substitute 'teeth' for 'mind' in a little thought experiment changing your post.
To say that the possession of teeth is but a function of a 'toothless' material body structure is also to say there must be a 'reason' external to this toothless body to be in need of teeth.
Successful mammals need teeth to eat prey and a brain to find it. There is no more need for a universal mind as there is for universal teeth.