Why is dirt called dirt?

Answer 1

Dirt is derived from an old middle English word, drytt that came from the norse invaders. It meant mud, muck or dung. It referred to the farmyard's contents in the fifteenth century.
Dirty in the sense of "morally unclean" is mentioned by 1599.
Dirt-cheap is from 1821.
Hemingway uses the term in the sense of gossip in 1926.

Dirt is synonymous with soil. Latin solium meaning ‘ground’ came to the French as sol then to English as soil "piece of ground, place" by the 13c. But another word from Latin is sus meaning pig. It was use in reference to pig wallows, and excrement. The French used the word soille means to defile, make foul or dirty, and wallow in filth. one more Latin word is solum meaning "mould, earth, dirt" Hence soil and dirt both refer to both earth and manure.

In the Oxford English Dictionary, ‘earth’ derives from the Old English eorde meaning "ground, soil, dry land", the Dutch aarde, modern Greek erde, and the original Teutonic erpa. While ‘ground’ is derived from the Old English grund derived from the original Teutonic grundu-z and the pre-Teutonic ghrntu-s.
The Latin humi meaning 'on the ground' gives us humus. This is exactly what we get when we compost manure; humus in the soil, better dirt.
One more word from latin is manu meaning 'hand' this gives us the words manual or 'done by hand' and manure or excrement. Manure was originally to "to cultivate land" combining this with Latin operi to "work" gave us manual in the sense of "work the earth" which in the fifteenth century meant "put dung on the soil".