It was canceled because viewership had dropped to the point that it wasn’t profitable to continue running. Plain and simple. Jewel didn’t do it any more than the new cast members of the X-files didn’t cause it to slowly die. It’s because the base concept of the show only allowed so many twists and turns before the audience decided that there was nothing more to say. Stargate has been alive in one form or another for a decade and a half. Let it go. Tune in for any new movie, but don’t expect it to be as awesome as the first however many years of the series when it was still fresh and new.