Even though Israel had seen the invisible God in action, they still wanted the familiar gods they could see and shape into whatever image they desired. How much like them we are! Our great temptation is still to shape God to our liking, to make him convenient to obey or ignore.
People became impatient and requested a god that they can see, and manipulated to their own favour. They wanted to rely on what they can see rather on what they can believe for.