Im theory is more simple they use filler just to give the manga alot more time gap if the anime is catching up to fast. The only filler that i enjoy are mostly comedy centeric ones.
That's kinda why I'm gonna try the filler out. I have a feeling both Bleach and Naruto' manga were being written with the anime in mind. Like half way through, they just threw character development out. Maybe in hopes of using filler in the anime to sell it. So the character development that should have happened in the manga is in the filler. At least, that's my conspiracy theory.
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