Marvel has a ton of cartoons on Disney XD. They are getting new, younger fans. However, DC Comics only has Teen Titans Go. This could be bad news, when these kids grow up. The kids who grew up with Marvel will read Marvel, while DC will be lacking a fanbase, since most of their fans will be too old to read their comics, watch their movies or whatever.
So why doesn't DC create a new DCAU? I know they've tried to create some superhero cartoons in the past that all failed (Young Justice, Green Lantern, Beware the Batman). But if they would have some cartoons that share a universe, when one cartoon ends, they can continue it with another superhero cartoon or something. Anyways, DC needs a new DCAU if they want to ensure their place in the superhero industry.