Why Fillers Don't Work

We all know that fillers are never as good as cannon. It's just common sense. What I'm talking about here is why they're never as good. Some of it is just because they have different writers than cannon but that doesn't explain why they get to be so bad. I think most of that is simply explained by the nature of fillers: they exist to fill time. That means they can't always be timed well since the studios only do them when they are running out of material to adapt. Bleach has had several long filler arcs that happen in the middle of other arcs and several mini arcs that just ruin the pacing. This brings me to the other issue that stems from this: they have to be a certain length. If the arc is too short they just have to make another soon after. That causes most fillers to feel dragged out when they could be halfway decent arcs if they were shorter. The last issue, in my opinion, is the fact that the animators don't know the source material as well and can end up creating plot holes later, like Zoro cutting steel in the East Blue Saga and Coby talking about passing over Reverse Mountain. These are my problems at least. Do you guy's agree? (I'll probably make another blog later about why One Piece fillers don't suck.)