Why was it cancelled? - Arrested Development (2003)

Answer: Low Ratings.

Technically it doesn't. Season 3 ended with every intention of coming back for a fourth season. But the show was canceled suddenly, so pretty much every character's fate is left open.

The Twilight Zone was about to be canceled after the third season, because Rod Serling took up teaching. However, at the half of the next season (1962-1963) another CBS show was canceled and TZ was put in it's place as a replacement. Because this show was an hour long, new TZ episodes had to be produced in this format. The resulting hour-long episodes are generally considered weaker, save for a few exceptions. This was due mostly to episodes becoming overly padded in their hour-long running time. The experiment was considered a failure, and the next (and final) season, the show returned to its original format.