The problem with the characters, in my opinion, is that the biggest superhero in the DC universe is basically without flaw, and practically unbeatable. Modern movie goers want to see frailties, even in our superheroes. It's tough to captivate an audience when Superman's only weakness is a glowing green rock. And I think that the other issue is that with Batman and Superman, everyone knows their origin story. It's basically canon at this point. There is no wiggle room for interpretation. We've all known their origins for over 80 years. I think the one thing that Marvel had going for it is that not nearly as many people know the origins of Iron Man and Captain America, who are far and away the two biggest characters in their movie universe. It wasn't a "been there, done that" situation. So even though these characters have been around for nearly 60 and 75 years, respectively, it was fresh in the minds of the movie going public.