Because Italy was lacking a single unified monarch as some other nations at the time had, their city states (Venice, Milano, Trieste ...) were allowed to trade and develop in independent ways. With this came independent art styles, culture, cuisine, etc. Despite all of these being pretty similar due to the small geographic differences. If they had had a powerful monarch rulling over all of Italy, there would be increased uniformity, perhaps even more wars as he would want to gain more land, etc.
