If you look at last year's roster, the team never went any more than 9 deep. Of those 9, only THREE returned - Jackson, Hawkins, and Sanogo. They're still 9 deep, but 6 of the 9 are new - Clingan, Karaban, Joey C, Newton, Alleyne, and Diarra. While they gelled really quickly early in the season, they never faced any adversity, so by the time the meat of the conference road schedule came around, that's when the growing pains started. Everybody still had to adjust to their role and their new team, even though they had been playing together for a few months by that time. And in conference, there is very little margin for error because the opposing coaches know your stuff by heart.
Not the point of this thread, but consider the 9 man rotations last year to this year.
Hawkins --> Hawkins: big improvement in handle, defense
Jackson --> Jackson: playing smarter
Sanogo --> Sanogo: an even more polished offensive game, adding the 3 point shot
Cole --> Newton: Better D, better able to get to the rim
Martin --> Alleyne: Step down in rebounding and toughness, comparable shooting
Whaley --> Karaban: Worse D and rebounding, but much better shooting and a better overall fit
Polley --> Calcaterra: Less size, but a much more well-rounded game (handle, D) and therefore, again, a better roster fit
Gaffney --> Diarra: About a wash, maybe slightly better D
Akok --> Clingan: Very different games, but obviously a much bigger impact from Clingan
Overall, last year's individual players had too many weaknesses that were too difficult to paper over with other guys (who themselves had some glaring weaknesses). This year's players are much better well-rounded individually and a better fit overall.