Here's the thing. The people who "hate" it so much used to like it at some point. Me? I enjoyed "most" of it up to the point of the 2 year filler of doom.
Now with Shippuden, there could be many reasons. One being that up to the point before the show. Many of the fans have already read the manga. And reliving the arcs again in anime form are turning out to be quite slow. Hell, many of the episodes turn out to be so boring that they just still watch just to mock the shit out of it. Another reason would be that many haters who still watch the anime still feel themselves to be commited to watch it. I mean come on, they watched this series from the very beginning. It would be kinda hard for them to let go. I know it wasn't for me since my reason of watching it still was just to only mock it. But now i have finally stopped once found out that a filler run was mentioned. I made that decision to stop that commitment right there. I do still read the manga.