Some of the moves have been for my career, or to get more schooling. Or, when I was a kid, were for my father’s career. (He was an internal auditor. They move around a lot.) I’m sometimes a freelance writer, sometimes a working artist, and sometimes I do telework, and I’d say my income from any of those things are generally helped and hurt in equal measure when I relocate. If my goal was to ascend a corporate/professional ladder, I suspect I’d do better by staying in one place and networking there; that would also be the smart move if I was an entrepreneur.
However, speaking about me specifically, the reason I didn’t mention my income as being particularly affected by moving is because when I was about 20 I picked a relatively modest discretionary income target, and try to hold that steady but increase my amount of free time. I do that even when I stay in one place. (The link between the art that makes me money and the art I think is important is weak and unpredictable, so I don’t like to rely on it for income, but also don’t want it to be displaced by the things I do for income.)
With regard to Italy, you are right that it’s becoming more common for young people to move out of Italy for work, and to a much lesser extent move within Italy. It’s still at a much lower rate than people in other countries move, and is offset by the people who never move at all. It’s very common to live with your family until you are married, or even afterward in multi-generational homes (where the parents have one floor, the grandparents have another floor, the adult children have another floor). Home ownership (as opposed to rental) is very high, particularly once you get outside Rome, and renters’ agreements are typically for four years instead of the U.S.’s one year, because there is an assumption you want to stay put. Even when people move for work, they often don’t fully move; they rent a room or an apartment in the city where they work, but return home to their house/spouse/parents/children in their hometown every weekend.