Books and Grocery are not an apt comparison.
Nobody needs to buy books and they are certainly not an immediate need like groceries.
Books are wants and it doesn't matter how long they take to ship.
They can also sit in the warehouse until the end of time.

That't not true for groceries, customers are going to the grocery store, because they often need something that day or are buying what they need for the week and the bulk of what they are buying are perishable items, produce, baked goods, meats, dairy, etc. These are not items that can sit around the warehouse and/or stay in shipping for days