1. Shipping cheese doesn't work. You might get lucky and get a cheese that hasn't spoiled, but there is also a considerable chance that the cheese won't be properly refrigerated during its travels.
2. Shredding exposes cheese to air, which, in turn, accelerates spoiling. Pizzerias can get away with pre-shredded cheese, because the distribution channel guarantees an extremely fresh product. Home bakers don't have this luxury.
3. Mozzarella doesn't achieve its full flavor without sufficient bubbling/browning. To achieve bubbling, the pizza must get plenty of top heat and bottom heat, and also must have a lower thickness factor, so it gets plenty of heat from below.
In other words, in order to judge any wholesale brand of cheese, it must be purchased from a distributor, in a block form, and be utilized in a setting with properly applied heat.