Doing It for the Art: Decode was commercially unsuccessful, but still produced a second season of excellent quality. Sadly, it looks like the series will have another cliffhanger ending.
No Budget: A borderline case. Second season budget was significantly affected with the commercial failure of the first one, with a lot of cutting corner techniques applied to compensate. The artstyle is much more simplified, with infamously sketchy episodes 7 and 12 (the very final one) and regular lapses in animation all around entire season, with only simple static cues suggesting actual action. Those lapses are extremely jarring when compared with fluid and detailed animation of the first season.