Gee, Supergirl ...
how can you tell?
Why is there a Jimmy Olsen at all? Seems simple to me: Jimmy is the Fanboy Personified. Poorly dressed, self-important, and inept, Jimmy is slavishly devoted to a superhero.
But Superman loves him anyway. And that is the secret of Jimmy's popularity.
Robin is cool; Robin deserves to hang out with Batman. But, face it; Robin is WAY cooler than we are. In fact, Robin is cooler than anyone else in the DCU. It's as hard to identify with Robin as it is with Batman.
But Jimmy? Well, not only is Jimmy not cooler than we are, Jimmy's not cooler ... than anybody. But nevertheless he hangs out with Superman and Superman rewards him with friendship simply because Jimmy has the ultimate fanboy quality: loyalty.
So, even though Jimmy is the stupidest person in the DCU (which is saying alot, in a universe that contains Lana Lang), he has his own fan club.
Kind of like Millarworld.