I’ve always wondered that. Because I think I read it in Blackest Night but to summarise;
Clark apparently wears clothing two sizes two big, slouchs and hunchs over and wears those glasses. So it’s to do with how he carries himself and how he presents himself so he has to be doing something mentally so that people don’t notices through those slight changes to his character that he his the same man.
Because we know that Clark is also regarded to be handsome and attractive, considering his exploits with women and he can’t always be in those clothes. So I think he lowkey uses basic psychology to change peoples perception of who he is but must also use something else so people don’t notice that he has the same nose, same chin and same lips as Superman because someone has got to either think ‘Familial link to superman because of similar facial characteristics that are usually hereditary’ or ‘HOLY SHITTING HELL, IT’S SUPERMAN’
And as we’ve seen from Batman; people will try and cash in on your secret identity or stick you in a city size prison to hopefully die. An from Green lantern we can see that people can recognise you from your basic face structure. So it would make sense that he somehow warps peoples perception of Superman by making his face appear different or Clark’s face different because those fucking glasses ain’t fooling anyone; Especially someone who’ve had sex with and has seen EVERYTHING -looks at Lois Lane and co-
Idk Superman has never been one of my favourite superhero’s anyway.