I think it has to do with 2 things:
a) A truly tznius woman would be embarrassed to have her picture publicized for all to see. Tznius isn’t just about neck-bone elbows knees. Its about staying out of the limelight and acting in a tznius matter. Rebbitzen Kanievsky would be horrified if her picture was publicized in a newspaper.
b) I think Shmiras Einayim comes in to play here. If its a frum newspaper, I doubt it wants to put men in the situation of looking at women. Even if they are tznius, a man should not be looking at women. Period.