This is not it, because if you look at the range of what is in shadow, it is significantly larger than the portion of the sky that you can see. If you could see that far, people in more of a 50% zone would be able to see the sky darken significantly in one direction and be bright in another. What we saw instead was the entire sky darkening evenly.

The real answer lies mostly in our logarithmic perception of light, meaning that we’re much more sensitive to the absolute change in amount of light when there’s less light than when there’s a lot. So the difference between 100% bright and 50% bright is a lot smaller to us than 50% bright and 0% bright.