Because unlike Marvel WB isn't under the illusion that they are guaranteed to make money, they've learned this the hard way. WB are plodding along at their own pace with comic adaptations, Marvel seem to be in some sort of rush for some inexplicable reason. WB has got the biggest comic franchise under their wing at the moment, it's raked in more money than they could have dreamed of and rewarded with several major award wins and nominations, if anyone at head office isn't happy with that there's no pleasing them. Superhero's aren't everything to WB, they've probably got a bunch of potential franchises up their sleeve, add to that the success of Inception may be a new factor to consider for WB, suddenly originality isn't looking so risky after all, in fact I willing to bet WB may be the studio that starts making more original blockbusters. I really don't think WB gives a damn about Marvel and what they're doing in regards to superheroes, in fact I believe some fans are trying to fan the flames for a war that doesn't even exist.