How many print reporters faces do you know?
Also Superman doesn't do many televised interviews or photoshoots so IMO most people haven't gotten a good look at both men.
The few people who have are Lois and Jon, the Justice League, Kara, the Kents (when alive), Sam Lane, Jimmy, and Lex even Perry doesn't have much interaction with Superman since post crisis.
Now Lois, Jon, the League, Kara, and Kents all know the truth so that leaves Jimmy, Sam, and Lex Jimmy two best friends are Superman and Clark so I believe he might subconsciously know but can't admit it to himself that "both" his best friends are lying to him. As for Lex and Sam I don't believe either believe Superman has an alter ego especially that of Clark Kent a man who usually neither respect.