The earliest form of storytelling probably consisted of simple chants. People sang chants as they worked at grinding corn or sharpening tools. Our early ancestors created myths to explain natural occurrences. They assigned superhuman qualities to ordinary people, thus originating the hero tale.
With the advent of writing, the use of actual digit symbols to represent language, and the use of stable, portable media, stories were recorded, transcribed and shared over wide regions of the world. Stories have been carved, scratched, painted, printed or inked onto wood or bamboo, ivory and other bones, pottery, clay tablets, stone, palm-leaf books, skins (parchment), bark cloth, paper, silk, canvas and other textiles, recorded on film, and stored electronically in digital form.
There are many reasons for this but mostly the reason is biological. Stories are hardwired in humans to be remembered over all other forms of communication.