I always wondered why nobody made the connection before. Always seemed like there was some sort of aura around Clark, not just of invulnerability, but of blindness, that nobody noticed certain things.
It always seemed simple to me. What happens to those who discover CK=S? With very few exceptions, they die horribly, lose their minds, become incapable of speech, wind up back in the fifth dimension, or other horrible fates.
I believe that their is a subconscious self-protection reflex in place. After all, galactically stupid is better than crushed under tons of rubble any day!