It is an excuse of why no one has explained how It arises.
Often when people talk about “complex brain = consciousness” it can actually be translated to “wow the brain is so complex, something amazing must be going on and it must have amazing powers (like consciousness)”. Usually there will also be talk about billions of neurons, feedback loops, etc.
The complexity is used as a scapegoat to blame consciousness on. We dont know how consciousess could possibly arise, so we blame it on some element of the brain that we dont understand. The complexity of the brain can baffle many and in discussions it can seemingly lead to an “open end”, as in “well, its possible”. And if its possible, then surely the brain does create consciousness do it. What else would? So the bafflement can cause many people to actually believe that the brain creates consciousness.
However, its quite simple to understand that it is actually not possible. To understand this, instead of looking at the most complex thing in the universe and trying to understand it while being baffled, one should look at an extremely simple situation. Heres how:
Imagine the fundamenal elements of the universe are: space + square blocks of matter. Remember these are the fundamental elements, so the square blocks dont even consist of atoms, they are just pure square blocks. Now imagine that you position 3 blocks on top of eachother. Does anything emerge from them? No, the blocks are just blocks in space. They do not have any property that allows the emergence of anything. Would it make sense to state that suddenly little glass orbs appear from the blocks? No. Now we position 10 blocks on top of eachother. Still nothing emerges. 1000 blocks. Still nothing. 10.0000 trillion blocks aligned in circular patterns, on top of eachother with tentacles intertwining to the core. Still nothing.
It is completely irrelevant how complex the configuration gets. The blocks will never do anything other than what is already contained in their fundamental properties.
The same goes for the physical universe that we know. If it does indeed consist of what physics tells us (elementary particles and fundamental forces), then no matter how complex a brain gets, or how hard you twirl a bunch of atoms around, consciousness will not come from it.