Star Wars: the Clone Wars Season 5 only contains 20 episodes when Seasons 1-4 all contained 22. There was no reason given, and there was a whole arc revolving around Rush Clovis that was planned. Is there any official reason given as to why?
The series was announced to be "winding down" by episode 20 of season 5, so it stands to reason that the show was effectively coming to a close. Also, at the same time Lucasfilm announced a "new direction" in their animation programming beginning with a new series in an era that has not yet been explored.