Supply & demand compounded by ticket requirements.
You want/need to be in certain place at particular dates and want the airline to enter into contract for those details. They will charge you such an amount for that contract with such rules. You break the rules the contract is broken.
You could book a RT USA-Switzerland and independent travel to and from Italy but you do so at your own risk of missing the return flight to the USA unless you give a large amount of time for problems. For me in such instances it's 1 day.