Our denial of God does not eradicate His existence. We are creatures, and we have nowhere near the power it would take to destroy God by our own words or thoughts. The deeds of the Israelites are all around them. They can hardly move without running into the fruit of their sins. There are thousands of illegitimate children.
Crime is rampant.
A powerful foreign enemy has successfully invaded and left them helpless to defend against further incursions. There is hardly an honest businessman left in the land. Cheating is a way of life. The mentally ill invade the streets, visible reminders of the personal fruit of degeneracy in the soul. And yet all of this is before God's face.