This works with basically any long running anime. Naruto, One Piece, FMA, Dragon Ball, you name it. But hey, why worry about condensing your plot when you can just make make episode after episode. And that still had nothing to do with what actually happens in that little bit of content.
You can describe the basic plot of Bleach in three words: Deus Ex Machina.
From Wikipedia: "A plot device whereby a seemingly inextricable problem is suddenly and abruptly solved with the contrived and unexpected intervention of some new character, ability, or object."For example: Ichigo becoming a soul reaper, Ichigo's Shikai, Ichigo's Bankai, Ichigo's Hollow Mask, Ichigo's... well you get the idea.
|And of course, I use the term "plot" when talking about Bleach very loosely.|
I'm pretty sure Kubo (the writer) just makes up stuff as he goes. If he happens to forget a character, a bit of detail, or major plot event along they way, he doesn't care, he will make money either way.
Then again, I do think everything past the first season should be considered filler. If it weren't for Byakuya and Renji, Ichigo would still be hanging out in Karukua Town killing hollows. And we all know how bad filler is...