Why do not all see God?

That is a good question.

Could there be a neurological reason? Could it be the result of how we're wired?

God is the absolute reality hence invisible

The unimaginable concept of God is not from the side of God. It is only from your side since it is your defect. Your imagination cannot transcend the dimensions of space to understand God, who is beyond space, being the creator of space.

God is the absolute reality and the space along with consequent creation is a relative reality. This point keeps God beyond space. This point cannot be sacrificed because the creation including space can be possible and under the full control of God only, if God alone is the absolute reality. If both God and creation are absolute realities, the control of God on creation becomes impossible. If both are absolute realities, you can see God in the space itself. But, there cannot be two absolute realities. Absolute reality can be one only. Otherwise, there is no possibility of creation. The concept of creation comes into the picture only when one absolute reality exists and creates the relative reality.

A real rope cannot create a real snake. A real rope can create a false snake as an illusion. Therefore, to see the absolute God, you have to make the world as another absolute reality and in such case the creation becomes impossible. All this is the technical difficulty in the process of creation and hence it is inevitable. If you understand this analysis, you will not mistake God as sadist troubling you by hiding Himself. All this analysis is given by Shankara.
[All these information are regarding the absolute God, but such God comes in human form to allow us to see Him, through the human incarnation]