Neither of them seems inclined to invent anything new, so why bother paying writers and artists to shit out Batman vs. Joker no. 3,644?
There is probably a figure that DC needs to reach that allows it to justify it's existence as a publisher of new print material, and it's probably more than just covering it's own costs. They may be reaching that point, otherwise why the desperate attempts to make big splashes, like New 52 and Before Watchmen?
Marvel may be the current king of superhero movies, but DC does make more and better animated shows and DVD's. Plus, there are a lot of movies made from DC's non-DCU graphic novels. They may be able to justify dropping the DCU print line and focus on just DCU reprints, New expanded Vertigo print publishing and a All-ages print line supporting their animated shows. Plus all the toys and t-shirts and other licensing.
The stable of characters wouldn't be any different than the Warner Brothers Looney Toons, and survive with just the animated and live-action shows and the occasional movie as the only new material.`
Maybe it's just easier to maintain the status quo, I mean, they are a small subsidiary, that makes them a ton of money in licensing. As long as they don't cost the parent company anything, they might be free to be left alone. How much of the licensing, stuff like the toys, statues, key chains, beach towels, underwear, floor mats, etc, how much of that is tied into the current comics?