There has always been a contrast in Italy between the north and the south regions, due to their varied history, in terms of economy, and not only.
It's not uncommon for a country (I would say it´s perfectly normal) to have areas with an higher concentration of wealth compared to others, but in Italy the contrast it´s particularly stark, possibly due to its very shape.
It probably has more to do with history than the shape. The Veneto, where I live, was an independent republic for longer than the United States has been a going concern. The south tended to be bandied about between various foreign powers, feudal states, and so on.
It's not uncommon for a country (I would say it´s perfectly normal) to have areas with an higher concentration of wealth compared to others, but in Italy the contrast it´s particularly stark, possibly due to its very shape.