We don't see God at work, because we don't know what we are looking for, or because we are expecting something different.
The same thing happens with the enemy. In many films, there is some portrayal of demonic activity: you see flames, and an ugly face with horns. You know it is evil, you know where you stand with something like that.
But in real life, what I experience is ordinary things - pleasure and pain, likes and dislikes, desires and opportunities. Natural things. But the natural desires can lead me away from God, can lead me into greed and lust and gluttony. Greed is natural, and is a desire for the good things that God has created and made available to me. That can't be wrong, can it? And even if it is wrong, it is natural. But there is - or at the very least, there can be - something of the demonic when somebody's life is caught up in greed.
We do not recognise the demonic influence because there is nothing supernatural happening (or so we think), and because whatever is happening has nothing to do with the demonic manifestations of the cinema. We do not recognise demonic influence at work, because it appears to be something completely different.
Similarly, with God. He is the source of everything that is good and true and beautiful. He is at work in everything good. If we do not recognise Him, that is our loss.
And if we do not recognise where God is at work, we fail to give Him the credit, to praise Him for His work. And we fail to respond, to join in, to be a part of what He is doing.
However powerfully God may act, you will only ever see something natural taking place. Healing, deliverance, conversion - it can all be explained in natural terms. You will never see anything that cannot be understood in natural terms, because your eyes can only see physical activity.
We have to recognise the presence of God in human events - His presence in an earthly baby, in a political dissenter dying on a cross. As we see, as we acknowledge His presence and His activity, so our faith is strengthened and we can see more of what He does, and pray for more to do done.