They haven't shot well this season, and their defense fouls way too much. That's it in a nutshell.
They don't have a low post scorer - Joe Smith off the bench is probably their best option down low, and Hinrich/Gordon/Deng have all been playing poorly to this point. If they don't shoot well, they don't win.
Defensively, they have been fouling teams way too much, and there has been a huge difference in the amount of foul shots taken so far. Teams attack the Bulls, the Bulls take jumpshots.
This team has started very bad over the last 3 seasons. Last year, they were 3-9, so while I do think they can turn it around, this should not happen on a team that is supposed to be a contender.