Why is it called hard cheese?

Natural hard cheeses get their taste, texture, and physical properties from high butterfat content, where the largest amount of fat and calories are contained.

A hard cheese, such as Cheddar, consists of roughly one-quarter protein, one-third fat and one-third water.

Hard cheeses are largely free of additives. Processed cheese on the other hand, contains a variety of additives such as dried milk powder emulsifiers and flavors.

As researchers have worked to reduce the butterfat content in hard cheese analogs, a decrease in flavor and in melting properties has also occurred. Lack of flavor is sometimes offset by adding herbs, peppers or smoke flavoring.

Natural hard cheese can be stored for extended periods but quality eventually deteriorates as the proteolytic and lipolytic activities in the curd become excessive. Storage life can be improved by processing. Decomposition of proteins and lipids results in a nutritionally defective product unsuitable for consumption.
Why is it called hard cheese?