Cost. I'll list some reasons why hours is often not possible. - Products can't always be fulfilled by the closest location. Especially for products that you ca

Cost. I'll list some reasons why hours is often not possible. - Products can't always be fulfilled by the closest location. Especially for products that you can't assume infinite stock of, this is a big deal, but in general there is an incredibly long tail of things sold. Look around the sites of Target, Walmart, Home Depot, and similar, look at what's in stock where. It's not universal coverage, and Amazon has much lower density of locations as well as higher SKU counts. If an order is split across multiple locations, it would be cheaper but take longer to first combine them at one rather than deliver the parts separately. - Last-mile efficiency. Stops are clustered and dispatched together, which reduces labor time and mileage. The total cost of 10 spread out stops could easily be the same as 40 more tightly packed ones, and the second won't be an option if they're out for delivery within hours. - Labor efficiency. There are a lot of humans involved still, despite the best efforts of these companies, and a bit of latency allows for consistent utilization despite hour-to-hour and day-to-day changes. Lastly, delivery within hours is offered. Walmart calls it Express Delivery, Amazon has Same-Day Delivery (as well as some 2 hour delivery), Target has Same Day Delivery. These are just premium services with limited selection because it's expensive to do, and modern Free Shipping is an illusion of shipping being too cheap to price when it really isn't. It's cost optimizations all the way down and still not enough.