Problem is when you lose players like Sully and to a lesser extent, Buford, you need to either backfill with immediate-impact recruits or rely on improvement from returning players to retain the same level of play. We don't have any impact new guys, and from what we've seen I think it can be argued that only one returning player has improved to any noticeable degree - Shannon Scott. Several players, IMO, have actually regressed from last year - notably Craft and Lenzelle.
So we lost a lot and gained little to nothing (I can't be pursuaded that Ross has become a real contributor yet). Combine that with what everyone is pointing out as a lack of floor leadership, and the falloff is considerable.
Two things to keep in mind, though - 1) there's still time for guys to improve this season and you have to believe that's at least possible for Amir (why hasn't this happened yet?) and Craft (based on the fact we've seen him as both an offensive baller and floor leader in the past); and 2) there was a ton of concern and frustrated threads last year about leadership and consistency, and we landed a few plays shy of the NC game.