Was canceled, not because of ratings, but due to the fact that the leads of the show didn't want to have the format of the show change from a single-camera show to a multi-camera sitcom style show with a live audience.
NBC announced drastic changes to the show for its third season. They wanted to switch the show from a single camera format to a multi-camera sitcom, probably because multi-camera show typically have lower physical production costs than single-camera shows. Furthermore, it was set up to explain the changed structure of the show by having Applegate, Arnett and Rudolph all playing actors who star in a fictional show-within-the-show called "Up All Night". Amidst the changes, series creator Emily Spivey and star Christina Applegate left the show. Despite looking for a replacement for Applegate, the series was eventually canceled.