Facepalm

It's ok for the average American family of two adults and 16 kids

Growing up my family would easily drink a gallon of milk or more per day between breakfast cereal and consumption with dinner. If my Mom made cookies, a cake, brownies, or some other traditionally paired with milk treat or something that itself used a lot of milk (such as say pudding) that day we could easily consume two gallons in a single day. So, if you have a large family (growing up mine maxed out at two adults and seven kids) or a smaller family that are heavy milk drinkers you could easily knock out three gallons before they spoil particularly if you start including things like being big fans of pudding, custard, mac and cheese, french toast, yogurt, milk gravy and other milk using recipes.

Now if it was a single person that is a lot of milk, I think I could probably power through three gallons of milk before it expired but it'd be deliberate high usage on my part and certain not "this is the amount of milk I want to consume" levels.