Why has Shirley Jackson chosen common people for her characters?

“The Lottery,” which was widely criticized when published in 1948, has become one of the most well-known and admired American stories of the twentieth century. Through this and other stories and through her novels The Haunting of Hill House and We Have Always Lived in the Castle, Shirley Jackson came to occupy a singular place in popular fiction among writers of her generation.
A professional writer who depended on the income from her publications, Jackson was conscious of the elements of popular appeal. Nevertheless, she did not hold back from creating terrifying scenarios and characters. The characters's apparent normalcy at the beginning of a work, which may be revealed to cover up a deep psychological problem, accentuates the fear they strike in the readers.
“The Lottery” somewhat deviates from this pattern, as the author does not present, much less analyze, any mental illness or deviance. Much of the tension in the story derives from the fact that the characters are conducting normal, everyday conversations. They neither experience epiphanies nor reveal any secrets that might help the reader understand why the lottery continues aside from tradition or why none of them stand up to opposite it. The matter-of-fact tone combined with the ordinariness of the characters implies that such an event could happen anywhere, that it could be carried out by anyone. “They” are “we.”
In The Haunting of Hill House, the normalcy of an array of characters underscores the unique role and, in some cases, gifts of each one. The sensitivity of Eleanor Vance to paranormal activities stands in sharp distinction to her quiet, introverted, modest demeanor. Each of the other characters, drawn from various walks of life, has a more notable connection to the otherworldly phenomena, but only Dr. Montague is a trained “ghost hunter.” As the novel progresses, it is the very ordinary Eleanor on whom the house seems to be focusing. The reader is more likely to identify with a reluctant participant in such an expedition and to be more horrified at her apparent inability to escape.