This is something I've always wondered, as most DC and Marvel cartoons tend to be short-lived, many being canceled at 26-52 episodes. There are exceptions and I believe Batman: TAS has the longest episode count (unless you count the entire DCAU as one show, but not really), and other action shows barely make it up to 100 episodes. The original TMNT cartoon lasted 10 seasons and made 193 episodes. The 4kids TMNT show lasted 7 seasons and made 156 episodes and a movie. The Nick cartoon is now renewed through Season 4, meaning it'll have at least 98 episodes. And given the Nick show is a success it'll likely go on for a long time after that, matching the episode count of its previous iterations. What makes TMNT cartoons last for 150-200 episodes? No other action cartoons in history ever last this long. You could say it was because the original 80's show was a huge fad, but the 4kids cartoon aired on an obscure network and still made 156 episodes and 7 seasons. And the Nick cartoon is a tremendous success. It's almost like TMNT is the American equivilant of shonen anime like DBZ, Naruto, One Piece, Pokemon that goes on for literally hundreds of episodes.