the main reason is because chiellini, bonucci and barzagli are perfectly suited to a backline of 3, i guess... i really can´t understand people who want to push chiellini to the left in a back four and play bonucci in the middle where he is obviously much less confortable. furthermore it just doesn´t make sence to play one of the top CB around out of position.
imo a back three with asamoah as lwb (even though it´s not his natural position) is way superior to a back four with either chiellini or de ceglie on the left.
i don´t get the hype around 433 anyway. obviously the 352 is more solid defensive wise and and i felt very disappointed with the attacking play in the derby before they went down a man. of course it´s just one game but somehow 433 fanboys are using exactly this single game to "proof" that 433 is great

.
nevertheless i can fap to a 433 with vucinic - dzeko - giovinco up front but imo we would need a class LB for that. on the other hand this would mean benching bonucci, asamoah and reduce pogba´s playing time... can´t fap to that
//edit: argh too late