[jesselt]

I don't think it is the length of the series that makes them drag on, but rather the fact that they are often kept in the dark about how many seasons or episodes they will get. They may start production with 10 episodes and the network will tell them half way through that they want 7 more, so the producers end up scrambling to add filler. I also prefer the method of just having a set number of episodes, even if the show gains or loses ratings.