Especially in long running anime series this is highly visible. They are often based on the manga as a source material. Eventually the anime will catch up with

Especially in long running anime series this is highly visible. They are often based on the manga as a source material. Eventually the anime will catch up with the manga and to avoid that the anime has to be stretched with "filler content". Producing an anime series requires a far far bigger team and is significantly more expensive than a manga so why is this happening in the first place? Why can't they just add more people to work on the manga? The artists are not the bottleneck. The authors of the story are the bottleneck. They have to come up with an original story and this is not the type of problem where adding more people helps.