Why larger cubic engines give low mileage?

Why larger cubic engines give low mileage?
not necessarily true.Larger cubic inches usually make more torque, but usually at the expense of mileage. Besides more frictional loss, you have to feed those inches. Sometimes you can run a higher gear ( lower numerically ) to spin the motor slower and ger better mileage. For example , Corvettes run bigger cubes, but can get close to 30 mpg by engine management, aerodynamics and gearing. Some of the big barge 500 cu. in. Caddies of the 70's and 80's were known for their outstanding highway mileage cause they were just barely loafing along.