Because it’s human psychology which has formed over the years of our lives. I would say, we are programmed as we have observed the elders doing the same around us. Remember when you were a child, do you used to blame God for everything small or big that used to happen in your life? No..right? As we grow up, we tend to imitate the society we live in and thus our mind starts sticking to that particular point, like in this case blaming someone else, without going in depth of that matter or without analyzing the situation we are in.
Our parents, grandparents, all the relatives do the same. Today, you can do a small experiment of asking them the exact reason about them always blaming God for anything bad that happens in their lives, and you will be shocked to know that they themselves don’t know the exact reason and will say something random which they have ‘learned’ from someone else which is, “God is everywhere and he is the one all behind this”.
So if you are claiming that God is everywhere and whatever he does is for your good, then why is it that suddenly he becomes the villain whenever something bad happens? This is all because of lack of understanding and thus the old saying, ‘half knowledge is dangerous’ becomes true here.
A simple solution to this is to not to think too much about the things which are out of our control and focus on the ones which we can surely do and that too without a single doubt in our mind, which will eventually change the perception about the things happening around. I would say, gratification is the key here as it is a force to take us towards the road to freedom, rest everything is a mystery and maybe God himself may be not able to do anything in certain situations (if at all he has the powers). So what to say?