Why the big gap in years?
Between Season 1 and 2...
shareWell the series was canceled in 1963 due to a dip in the ratings, but it lived on in reruns. For the rest of the 1960s and all through the 1970s, more and more people watched it, giving it a cult following. They ran it on Saturday mornings and by the early '80s, ABC decided to bring it back, so they retooled and produced new episodes from 1984 to 1987.
Similar to Family Guy, it was canceled in 2002 but developed a cult following and due to massive audience response, it got revived in 2005.
Futurama, same thing. Canceled in 2003, huge cult following, audience responded in droves, they brought it back this year.
Reason being that cartoons are cheaper to produce than live action shows.
It's also the nature of tv in general. Lots of shows get cancelled even though they get relative good size-audience. But put yourself int he shoes of a tv executive, you know your job isn't a permanent one, would you rather take a chance on renewing a show that did alright or take a chance on a new one that could be great?
All in all like The Jetsons or Family Guy for examples they can find huge success in re-runs where the fanbase grows and it gets to come back. Sometimes in the modern age it's only a comeback in terms of coming to DVD or Bluray but for some whole new seasons get to happen when the right ingredients are mixed.
I refuse to argue on IMDB until the general populous actually uses their brains