Frozen pizza usually contains preservatives and chemicals to make sure the pizza survives its stay in the freezer case. As far as I know, pizza you make from scratch---at home or at the pizza restaurant---does not.
I'm reading the ingredients of Digiorno and I don't see any preservatives
There is a lot of stuff listed for each ingredient (some may or may not be for preservation purposes), but if I bought those ingredients to make my own, they'd be in those ingredients.