I don't have a definite answer, but allow me to indulge in some historical background. The political-economic structure and history of Northern and Southern Italy are vastly different.

The North, once part of the Holy Roman Empire, was fragmented into many small city-states, republics, and principalities. These states were heavily involved in the arts, science, banking, and trade, and well connected to West-Central European political, economic, and military affairs. They were minor players, and sometimes the battleground of, various European conflicts, in which France and Austria became influential powers there. Northern Italy was involved in the Industrial Revolution and remains a center of manufacturing and finance, particularly Turin and Milan.

The South had long had a more unified, but less effective, political system. From the medieval period onward, after it had changed hands between the Byzantines, Arabs, and Normans, it was controlled by Spain. I think there is a case to be made, that the active political and economic life in the Northern Italian states diverged from the South over this long period of stagnation under Spanish rule. The Industrial Revolution largely passed over this region, which became severely economically depressed in the late 19th century. To this day, although it is a modern society by any measure, Southern Italy has a much lower GDP per capita than Northern Italy and is more comparable to Portugal, Greece, or rural Spain. It remains dependent on agriculture and subsidies from the North. It also remains plagued by organized crime and corruption.

I highly recommend Robert Putnam's Making Democracy Work. It is both broad and dated, so there might be more timely and nuacned work on this topic, but it more or less addresses your question.

There was a few decades in the early-to-mid 19th century where the south was actually far more industrialized. Naples was the third or forth largest city in Europe, and some two-thirds of all money in circulation on the peninsula was Neapolitan. The Kingdom of the Two Sicilies had launched the first steamship in the Mediterranean in 1818, and the laid down the first railway on the Italian peninsula in 1839, but the late 1850s both areas of development were highly limited, not due to economics but due to politics.

After the Revolutions of 1848, King Ferdinand II of the Two Sicilies attempted to implement a policy of isolationism in order to avoid being over-run by the same liberal movement (in the classical sense of the word, e.g. one who would advocate both laissez faire free markets & the expansion of political power to the masses) that had almost toppled his rule during the 1848-49 Revolution. This meant that while the rest of Europe was opening up to the ideas of free trade, led by the British Empire, Ferdinand's Neapolitan kingdom was attempting to pursue a course of protectionist mercantilism. The Two Sicilies raised the tariffs on imported steel up nearly 25%, provoking retaliation by France, Britain, and the German states, over the agricultural exports of the nation, the prime source of government income. Olive oil in particular, which was used not only for wine and cooking but also as an industrial lubricant in most machines of the time, was hard hit by the tariff wars. This almost meant that Neapolitan industry was also affected. By the 1850s while Naples had some 100 kilometers of rail across the whole of the kingdom, the Savoyard's kingdom in North Italy had over 800 kilometers of rail in Piedmont alone.

Acemoglu and Robinson's "Why Nations Fail" may to some extent be applicable in comparing North vs South Italy.

Holy Roman Emperor Frederic II declared the region of Puglia to be the breadbasket of the peninsula and famously said "Grana et Vina dat", which the town of Gravina (where he built his castle) is named after. You could say that the entire South of Italy is a land that is excellent for growing easy crops.

Now, according to Acemoglu and Robinson's theory, countries with rich natural resources - including climates which make them good for growing easy crops, as is the case in South Italy - tend to have had "extractive" institutions set up, which are dedicated to siphoning the wealth of these resources to the central government and then letting the people who control the government take them. We tend to see this in the third world, where it used to be colonial rulers that set up these "extractive" institutions, followed by the dictators who replaced them and used the same institutions for policymaking, but it applies just as much to the less developed parts of Europe that have a history of "closed" government.

By contrast, countries without easily accessible resources need industry, education and actual wealth creation in order to enrich those who control the government.

So, more "inclusive" institutions get set up to maximise this, which create an environment where wealth is created rather than simply extracted. This is true in places like Britain, Germany and the north of Italy. Notice how, for example, the oldest universities in Europe are in Oxford, Trier and Bologna.

One thing I'd like to add to what's already here is that after the Risorgimento, the Italian state typically viewed northern and southern Italy as separated by a perceived ethnic/cultural difference that precluded the north being more "developed" in terms of industry.

Two good books on this subject are Nelson Moe's The View from Vesuvius: Italian Culture and the Southern Question and John Dickie's Darkest Italy: The Nation and Stereotypes of the Mezzogiorno, 1860-1900. The titular "Southern Question" in the former was a view constructed as a kind of nationalist narrative and a shorthand for discussing Italy's modernity vis-à-vis other European nations that didn't quite conform to the regional reality. This prompted a series of bureaucratic state projects in order to "civilize" southern Italy, and the stereotype of the rustic, somewhat barbaric southern Italian (Sicily in particular) still exists today.

A really telling cultural example is the opera Cavalleria rusticana, or "Rustic Chivalry," by Mascagni. To be brief, the plot involves a vendetta arising from contention for a woman's favor, culminating in a knife duel. It was wildly popular when it was first performed in 1890 (further north, of course) because of the perception that southern Italians were "hot-blooded" and had archaic notions of honor and tradition not befitting modern society.