Well, if the comics were too logical none of the stories would ever have lasted this long. It may be that no one expects Superman to have a secret identity since he does not wear a mask, so they are not looking for another identity. The characters of Superman and Clark Kent are also two drastically different personalities. Spending time with the bumbling, mild-mannered reporter, no one would have guessed him to also be the charismatic, charming superhuman Superman.