This is just speculation on my part, but I was just watching some old episodes of Duck Dodgers and rewatched "The Green Loontern" where Daffy meets the Green Lantern Corps and meets Hal Jordan and even becomes a member. It reminded me that Paul Dini is no longer writing for DC cartoons, but Marvel. Paul Dini was a producer/writer on Duck Dodgers and writer for multiple DC superhero shows including Batman:The Animated Series and Batman: Brave and the Bold. Paul Dini is now on the super fast paced Ultimate Spider-Man which has some faults I'll bring up shortly.
So here's Paul Dini, whose been working with DC and Warner Bros Animation for years and you have this new Green Lantern cartoon coming out with character designs from Bruce Timm, who Paul works with all the time. Then you have no involvement with him on the Green Lantern project? It's a bit odd. He must have enjoyed Green Lantern enough to get it into Duck Dodgers for whom he produced and wrote. Yet, there's no episode he's writing.
I could be wrong and Marvel got to him first and now he's just too busy or he signed some sort of a contract where he can't work with competing shows while on his. It's just a bit odd that he just stepped away from DC/WB. Might just be a big bag of money.
The argument of only using new blood on the show doesn't make sense, because they didn't take a chance with another character designer, they took Bruce Timm's designs. The people in charge aren't that new either.
On the subject of Green Lantern, this quote from Sam Register who basically takes any old property owned by Warner Bros and updates is kind of sad with his thoughts on the Green Lantern show.
"We can’t wait to show the world this fresh take on an iconic hero—one that represents not only the first Bruce Timm series to be produced in CG, but also the first time Green Lantern has been rendered in CG"
It's the first time someone rendered something? What does that have to do with anything? CG doesn't magically make things better. I still don't get why they chose Red Lanterns over Yellow Lanterns and ... there's just too many things, but frankly my problem is Hal Jordan shouldn't have a team. Just like Spider-Man.
For Ultimate Spider-Man you can thank Disney for paying for quality animation. Marvel picked some of the worst animation houses for previous recent animations. Wolverine and the X-Men was I believe from a European animation house, as was Fantastic Four to save money by not hiring US animators. Spectacular Spider-Man's ugly design and animation house hadn't had anything as big as the Spider-Man property, I think it was straight to DVD market company. Even in anime, they chose Gonzo which is facing bankruptcy and I consider them one of the worst animators in Japan. It also falls on Gonzo for having incredibly interesting starts to their series, but all their animes suffer from becoming boring and slow paced immediately. Some of the worst endings, I've ever seen.
Ultimate Spider-Man's animation is thanks to the team of Man of Action a group of writers/comic book artists who did Generator Rex. They were also plucked away from CN/WB by Marvel/Disney. I think it was bitter, because Generator Rex last episodes still haven't been shown in the US. They might be up on iTunes. They are completely finished, so no reason not to show them.
Ultimate Spider-Man's problem is his team-mates. He doesn't need them. He's Spider-Man and angsty teen with no one to turn too. The show is too jam packed with them. They don't add anything. Some recent episodes don't even involve them, which is a bit strange, because their suppose to be his back up. They weren't there for Venom or Hulk. I just don't get their point. White Tiger, Power Man, Nova, and Iron Fist is such a bizarre sampling of heroes to choose. Overall those team mates aren't needed for Spider-Man to overcome whatever villain is out there. They also aren't helpful and seem to be crappy generally.
It being right next too the Avengers cartoon also adds to the confusion as the same characters are different ages, act differently and talk differently. No need to worry as the Avengers is most likely cancelled by Jeph Loeb, which sucks, because the show is great and fits the damn movie series.