Btw: taking the boat from Messina to Villa San Giovanni is quite a nice experience. There is a tradition to eat arancini while crossing. Most Sicilians are not actually hoping so much to see this bridge to be completed, especially since in Catania and Palermo there are very high traffic airports with plenty of cheap options to go to Rome or Milan (Catania airport is the 3rd by number of flights in Italy). If the fast trains available in the North would be available here, it would be different perhaps.
About the social factors, if the bridge would start from Catania, where I live, I could be a bit more positive about the ability to complete it. Catania has kinda of a different mentality compared to the rest of Sicily (I guess I can tell this without biases since I'm from the center of Sicily and lived in multiple places for years). For instance Catania is the only place under Naples to have a subway. Apple and Ikea are in Catania, and so forth, in general you can make things work here, and even if this is a national project, local factors may play a role. Messina is not similarly well positioned.