Most western cartoons are self contained episodes tho, while there is a general recurring antagonist, the conflict has to arise, develop and be resolved within the same episode. Very rarely you get multi episode arcs. Sometimes you get overarching storylines as a driving force that span whole seasons, but the main conflicts remain episodic. Spongebob is still working in the Crusty Crab by the end of the show, Kim Possible is still fighting Dr.Draken and Shego by the end of the series, Homer is still working in a Nuclear Powerplant, etc..

Anime is different in that regard because the story is laid out from start to finish usually over the course of 10-20 episodes. Whether the story has actual substance is a different question. But the thing is, anime can get away with an episode were nothing happens as long as it drives the plot towards a conclusion. But a children's cartoon where for a full episode nothing interesting happens usually won't even leave the storyboard.

That's why "filler episodes" are usually an eastern anime instead if a western cartoon trope.