You could say the same about Germany where there's also huge regional differences (even bigger ones due to religion).
It's very hard to imagine European and world history without a united Italy.
Italian unification success was one (albeit not the primary one, which was the rivalry with Austria) major source of pressure on Prussian elites [1].
We look at history at very abstract level, but in 1861/62 Prussian newspapers were all into "look at how Cavour did in Italy, unlike that incompetent Bismarck".
Then again, if Italy still was 3-4 separate states, I don't think they'd be up for merging.
People are pretty conservative with these things.