Often we ask "why." We expect an answer. Many people reject God because they cannot find an answer.
They reject the notion of God because they cannot accept their limitations. They cannot accept the issue is that they cannot find the answer to their question.
Ultimately in life we meet many questions we will not answer. There are many times we do not know why something happened or what would have happened.
A lack of clarity is not a reason for unbelief, but rather a reason to accept our limitations. The goodness of God is not dependent our our capacity to grasp a reason for things.
We often like to tie the world into a pretty box. We wish to do so by cutting corners and eliminating mystery. In the end we have more unanswered questions and the box is not pretty or complete.
The box without God is held together by a belief in progress which has little basis in reality. Yes there is progress in some areas, but you often see massive regress in other areas in society.
The problem is that the condition of the human heart manifests itself in every generation.