A modern interstate leaves few excuses for missing our designation. Every few miles interstate signs tell us what is ahead. As we get closer, the signs get closer, and the last sign tells us to turn. The writer of John recognizes that the Hebrew nation has missed its destination. He writes to help them recognize they are lost, and to help them see the need to correct their path.
He wants them to know that God is not to blame. Just like the interstate signs, God had been giving them signs throughout history of the coming Messiah. The Old Testament is full of revelations about what they should be looking for. They failed to understand, or they failed to be observant. No matter the cause, they were living in darkness.
John tells them that God went beyond the Old Testament revelations. God sent a man to witness to them in person and point them in the right direction. John the Baptist came to testify concerning the light that was coming into the world. Just as Fourth of July fireworks are announced weeks ahead so people can be prepared to watch, God sent John the Baptist to announce to the Hebrew nation Jesus was coming. Many did go into the desert to hear Him, and some of them believed that he was the Messiah. He was not, he was but the announcer before the main attraction.
John was writing to people who remembered John the Baptist and respected him as a prophet. In spite of that, they still did not recognize Jesus. Some did not recognize Him because they were not looking for the right things in the light. They wanted a light to blind their enemies, God gave them a light to illuminate their sin and their need for repentance. Others did not recognize Jesus because they refused to look; they loved darkness.
A missed exit requires us to turn back. Christ the Light still shines; people can repent and recognize Him or they can continue living in darkness.