The first and foremost reason the majority of people are deceived is because of the god of this world. satan, the father of lies and ruler of the world governments has used a brilliant deception in twisting Gods creation. His job is to lie, steal and destroy. By creating this monumental lie, humans disconnect from the Creator and his creation. Millions if not billions of people have been duped into believing that we are merely here by accident, mankind evolved from apes, and we are spinning in the middle of nowhere with no purpose.
In their case the god of this world has blinded the minds of the unbelievers, to keep them from seeing the light of the gospel of the glory of Christ, who is the image of God. 2 Cor 4:4