Why did Italian families in the early 1800s Change their last name?

My 5x great Grandma Maria Domenica (1808 abt) went by 2 last names (Mezapelle and DiBartolomo) at first I thought her dads name was Bartolomo and that was why she put (DiBartolomo) but I have 2 documents saying her dads name was Antonio so I don’t think it’s that, so I dont understand why she went by 2 different last names, on One record she uses both of them. Does anyone know why? There’s also other examples of this in my family so I don’t know if it was common also: (Penne Pescara Italy)