Which is a classic case of quality over quantity.
Producing animation takes a lot of man power, there is animation, story, music, sound effects, coloring, acting, and so on with a typical show. Which may not sound like much, but it adds up fast. For a quick short, this is hardly an issue. But for long lasting series, this type of thing will eventually strain on the quality and ideas start to run dry. Hence why long running series like Bleach and Naruto tend to have noticeable drops in animation and a lot of filler.