Mostly because the series are good. This is almost instant fail nowadays. I'm still very amazed that Battlestar Galactica was allowed to run it's full course. The Sarah Connor Chronicles were in my view good, but not good enough. There were a few points in the story they could barely make stick, like Sarah Connor asking a latino gang about 9-11. By the time the story got to that point, they were in the future long enough to find out for themselves what happened well before. For a bunch of freedom fighters they surely dropped the ball... the first thing you do when you arrive somewhere is getting the lay of the land... Also, the SG-T says she has been busy cordinating the build of the timemachine, so it follows she has jumped back and forth through time and as such should have superior knowledge. Yet, nobody asks her anything and muddle on through. The Summer Glau terminator smiled and acted like a normal girl in the classroom, but after that, she didn't move a facial muscle ever again anymore. That irritated me to no end. I think that the story was driving into a dead-end at breakneck, so pulling the show was prolly a wise decision. Who needs another Twin Peaks?