Why aren’t the superheroes delivering audiences this summer? Dropping more than 65 percent in its second weekend from an inauspicious $52.3 million premiere, Warner’s DC Comics-based “Green Lantern” proved that moviegoers’ appetites for superhero fare has mortal limits. (Though Warner is already developing a sequel.) “Thor” fared much better, but it’s not the hit other Marvel properties have been. Same for the reboot of “X-Men.”

