I think the issue is that animation isn't taken as seriously in the USA. It also doesn't help that every cartoon nowadays has to be a goofy comedy, so action cartoons are dying. I don't HATE Teen Titans go, but I have to admit that I am a little salty that the other shows of the DC Nation cartoon block had to die. I would have loved to see where Green Lantern the Animated Series and Beware the Batman (despite Batman fatigue) would have ended up. When it comes to the DC animated properties in recent years, the pendulum swings heavily in both directions...we have either gore fests or booty songs. I like the Harley Quinn cartoon...but that falls into comedy. I still like Young Justice, even if the last season was going out of its way to remind us it's not on Cartoon Network haha.

Marvel animation has to be "for kids" in a way that they actively went to kill the "all ages" cartoon that they had (Avengers EMH) and replaced it to ape the movies more (which I guess EMH was meant to do originally...but it kind of steered off into it's own thing).

Animation and live action have different strengths and weaknesses...I love the gaudy comic book costumes of most characters, but in live action they'd look silly...thus why X-Men don't have their more outlandish outfits. You could suspend your disbelief more in animation...though I won't say that live action hasn't tried...