It isn't really. DC has embraced "gritty and dark" as its main ethos for decades now. After
Watchmen and
The Dark Knight Returns came out to such acclaim, they've been trying to copy those successes ever since. The comics coming out these days are just as dark and violent as the movies, if not more so.
Last year, I was at a local comics-convention sort of thing, and there were copies being handed out of a Free Comic Book Day release sampling
Future's End, this big crossover DC was doing set in an alternate future. I couldn't even get past more than a few pages of it, since there was so much gore and death and violence -- there were these killer robots that were killing heroes and incorporating their victims' body parts into their own structure or something, and the last straw for me was an image of Black Canary's severed head stuck on one of the robots' bodies. (No, wait, I looked it up, and it turns out it was actually a Brother Eye-controlled Frankenstein's Monster who'd sewn her head into his chest, which makes it even more troubling.) Think about it -- the purpose of Free Comic Book Day is to attract new readers, including young readers, by giving them free samples to whet their interest, and DC's idea of how to do that is with this kind of relentlessly grim, disgusting violence porn.
Dawn of Justice looks positively upbeat next to that.
By contrast, the recent Marvel comics that I've either read or read about have much more of a sense of fun. After all, DC is trapped by its self-consciousness, its desire to prove itself mature and sophisticated, which is largely a result of its enduring need
to imitate Marvel. Whereas Marvel, well, already is Marvel, and thus doesn't have the same insecurity or uptightness.