How are you defining delivery? Packages going to the same address? I live in a development of ~100 unit apartment buildings. It will literally take the UPS/FedEx truck all day to go less than a thousand feet through the development, and in that time they're delivering hundreds of packages.

Also, Amazon has a large number of different warehouses that products are shipped from, and it's quite common for different items/orders to not ship together either for that reason or because some items' availability would slow down the others.