DC wanted to address problems that the characters have always had, such as Superman and Wonder Woman being unapproachable paragons and ideals rather than having personalities or costumes such as Superman's underwear or Wonder Woman's iconic costume being so iconic that the sex industry uses it. Superman seems pretty Marvel-like now and Wonder Woman is more warrior-like and is capable of killing her enemies. That explains the main heroes.
The JSA is said to exist on another earth now. They are supposed to be getting a mini-series soon.