Culturally, many contemporary societies in Southern Europe -- including places like Italy's boot, Spain, and Greece -- place a strong emphasis on family and don't subscribe as much to the brand of fiercely self-reliant individualism manifested in America that evolved from the 'protestant work ethic'.
I'd say it's mostly because we're fucking poor. France isn't protestant either, yet they leave the home much earlier. Looking at the map, it seems to correlate pretty strongly with income: http://i.imgur.com/KIPcRbM.png
Socioeconomic analysis of Italy normally sees a distinction between the wealthier, more industrial Northern half (e.g. cities like Milan) and the poorer, more agricultural, mafia-troubled Southern half (e.g. Naples) normally including Sicily and Sardinia too. A rough line for the split could be about the latitude of Rome.
"Italy's boot" here corresponds to this Southern Italy.
