In my opinion, i think we usually don't play a 4-3-3 formation because of the type of players we have. Firstly, Bonucci can't play at a high level in a formation with 2 CBs, the role of sweeper that he actually plays exposes him less than in the case of a 2 cbs formation. Also, we don't have proper wingers for a 4-3-3. Tevez and Osvaldo will be wasted in such a position and Giovinco can't defend.