Italy has an older population with a greater percentage of adults over the age of 65. We do know that the mortality rate associated with coronavirus infection is increased in those aged 60 years and older, and increased each decade thereafter. In addition to this, smoking is one of the risk factor for severe type of corona virus disaese and in Italy around 21% smokers are there.
In addition to those causes above, Italy tends to have more social integration of elderly and mobile/traveling cross-sections, they have several traditions that such as outdoor markets that encourage interaction across sectors in ways that would allow virus to be spread. Public espresso in the morning, after drink works, etc.