Please read “E1. Meaning to the Meaningless” before reading any of my other articles on Ecclesiastes.
Ecclesiastes 8:10-17

To Solomon what God is doing does not make sense. Solomon knows that if you reward a person for good behavior their behavior improves. He knows that if you punish bad behavior you get less of it. He also knows that when authority does not quickly carry out the punishment, the bad behavior will continue, and will become worse. Since he knows this, he is sure that God also knows it. It is only logical to believe that life will go better for the righteous, and that God will punish the wicked. He observes the world around him expecting to find that this is true. He does not discover what he expects to find. He sees wicked people who commit hundreds of crimes and still prosper and live long lives. He sees the righteous get what the wicked deserve.

Why does God not punish bad behavior quickly? Why does God not reward those who fear him, and who live righteous, with long life and prosperity? He looks for answers and cannot find any. He decides that what God is doing does not make sense, and no one can discover its meaning. It is beyond human comprehension, and even if other wise men claim they know, they cannot really comprehend it either. Therefore, it is better to quit worrying about good and evil. Humanity should just eat, drink and be merry until they die.

Solomon had a good understanding of the nature of humanity, we do respond to reward and punishment. He did not understand God it all. If God only cared that humanity behaves correctly he could have put us in shock collars. He could have created us without freewill; He did not. He created us with the freedom to choose right and wrong. The Lord is not slow; he is patient with us, not wanting anyone to perish, but everyone to come to repentance. (2 Peter 3:9) The world has problems not because God is slow to punish, but because we are slow to repent.