But, yep, like @Christopher said, the real reason is they wanted just to use the old well-tested "Secret Identity" trope that worked so well from Zorro to Superman tv shows. If you think about it, it's handy because when you run out of ideas, you can safely pad the episode runtime with some shenanigan on how our brave hero manages to hide his secret from the only intelligent woman in the show, who has to be put back in her place.