Does anyone know why there isn't any two country Italy/Switzerland pass?
No, I don't know why. However, while a railpass can be a good deal for Switzerland, that is not true for Italy. With a pass, if you take any EuroStar Italia trains, you will have to pay a reservation fee of 15-20 euro. Point-to-point tickets will be cheaper, particularly if you buy your tickets for fast trains a day or two in advance and get an Amica fare (20% discount). If any of the allotted seats are available, you can get an Amica fare up to midnight of the day before departure. (Amica fares are not offered on cheap regional trains.)