People are so used to Amazon Prime that they have no idea what things cost to ship any more. I run a small online store and every 1-pound package I mail out costs $8-12 in postage by the cheapest shipping method available to me, at commercial shipping rates. If the box is over a cubic foot in size and going to a state on the other side of the country, it can quickly double or triple in cost.
Amazon has $120/year in Prime subscription fees to subsidize the displayed shipping costs, puts some of the shipping fee into the item price (they're rarely the cheapest for most products, especially very cheap or very heavy ones), has a warehouse within 20 miles of every American so that nearly everything they ship is a same-zone local shipment, and has their own delivery network so they don't have to pay carriers. No other business has those things.