Bleach had *a lot of fillers*. The first filler arc wasn't that bad and they tried to fit it in more neatly.
And then, they kept catching up to the source material (despite the creator even conjuring up an arc or two to keep the anime going).
Instead of postponing the anime until there was new material (something they ended up doing anyway), they kept inserting inexplicable filler arcs set in parallel universes in the middle of major battles.
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Bleach also winded up being a classic case of creator burnout where the creator was expected to keep putting content out (I think it was every week) and he just couldn't do it.
As far as anime are concerned now though, I think the model of putting content out every week is more or less dead at this point. If there's content, it gets adapted, otherwise it'll resume whenever there is content.