Plain Chant is often the most common form of story telling as it consists of grand, often exaggerated myths and legends. It is very specifically written to create the most exciting imagery possible and to draw the listener deep into the story. For this reason most plain chant stories are meant to be recited word for word, with little variation even down to tone of voice, speed, rhythm and possibly actions performed (though many of these specifications may vary from story teller to story teller).
Most Plain Chant can be reasonably compared to a form of free verse poetry. Stories are often shorter than High Chant, so they are usually preferred in common rooms where lower class listeners either don't have patience enough to listen to the long, artful (and usually philosophical) stories written in High Chant, or they are called by farms and other duties, causing their amount of listening time to go significantly down.
While bards residing in great halls and palaces typically are drawn to the study and memorization of High Chant, gleemen and the like (bards of the lower classes in a way) naturally focus on Plain Chant. Though gleemen will often memorize several stories in Common Chant for use in casual conversation, Plain Chant stories are memorized and recited more commonly than both High Chant and Common Chant (though it is possible that High Chant may be contained in more books and other written forms).