> milk delivery subscriptions used to be common. when you'd cancel your membership, they'd just stop delivering. they didn't come back to repossess your unused milk.
No, because they charged you $1 for every bottle they delivered. You bought the entire bottle upfront (you may have paid in arrears, but when it was delivered you agreed to pay)
Imagine instead the milkman drops 10 bottles on your doorstep. Some days you only want 1 bottle for tea and a bit of cereal, but other days you make some pancakes and need 6 bottles. At the end of the day the milkman takes back the unused milk and charges you for what you used.
Aside from the problem of milk spoiling that seems a perfectly reasonable model.