As a general rule the difference between Italy and France is historical. France was/is a large country run out of the center (Paris). This meant troops had to be able to reach the outskirts of the country fast to defend/attack. That's why slopes are 7-8% max, as that's the maximum gradient horses can pull cannons/provisions.
Italy used to be a bunch of city states (Roma,Genoa, Venezia, lots of smaller ones). They wanted to make it as hard as possible to invade, so they created roads with a gradient of 9-10%.
And in the US/Canada, roads have 4-5% gradient, that's ideal for the trucks.