The gabelloti-embody-mafia view arose from Fascist political expediency. [causal]
The view that the two groups coincided is of uncertain origin. During the early Fascist era it seems to have become predominant: according to Duggan (1988: 78), the representation of the gabelloti and their armed men as the embodiment of the mafia, and the fact that they became the prime target of the energetic action of Cesare Mori, Mussolini's prefect in Sicily from 1925 to 1929, may have been the result of simple political expediency.
XREF: Connects to the broader historiography of Italian Fascism using the mafia as a political target.
Diego Gambetta, The Sicilian Mafia The Busi…, loc. 856