The reason is that most people know almost nothing about chess. They might know basically how the pieces move, but that's it. Personally, I never can tell the difference between the king and the queen.
Although I've been called things like "smart" and "intelligent," I don't play chess, I don't like playing chess, and I wouldn't know an invalid layout if it bit me.
"For shame, gentlemen, pack your evidence a little better against another time."
-- John Dryden, "The Vindication of The Duke of Guise" 1684