You pay more to get more. Renting a four-bedroom townhouse is far more expensive than renting a studio apartment. The nightly rate for a penthouse suite is much higher than for a standard room.
So, in ocean shipping, you might expect booking a load of coal on a mammoth dry cargo vessel would cost a lot more than on a bulker carrying less than a third the volume. Or that a spot voyage deal for a supertanker carrying over twice the volume of crude oil, or a product tanker carrying over twice the gasoline, would be way more expensive than on a smaller ship.
