Yeah, the reason Sicily didn't develop wasn't because of mafia, it was because of Bourbon mismanagement. Charles di Napoli was one of the greatest kings Naples ever had, but his successors couldn't match his success. Instead even though they were the richest and largest Italian state they succumbed to terrible mismanagement and decline whereas the North didn't. Also another thing is the North was originally many city states that all competed amongst each other and became highly developed as a result. The south meanwhile only even hosted Amalfi which didn't last too long and throughout the medieval times was pretty much under one or two kingdoms (there were exceptions). Not to mention of course that the Po Valley is pure gold in terms of potential for population growth, meanwhile the south though still Mediterranean in climate is much dryer.
Sabaud mismanagement played a big part as well.