We only offer one flat shipping rate regardless of the chosen shipping method. The shipping method is chosen later according to size, value and contents of your shipment.
The fee include not only the actual shipping costs, but other sales costs such as shop fees, banking and payment fees, packaging material, accounting fees or transport to the carrier.
For smaller orders, such fees still occur and would lead to higher costs than the actual revenue while for greater orders, the revenue compensate more of those costs.