This is a good question. We have to realize that "The Lottery" is a short story. It has less than 3500 words. This means that she needs to set the context and setting quickly. Arguably the best way to do this is to narrate what the town is like and what the people are like. This is exactly what she does. Consider her first sentence:
The morning of June 27th was clear and sunny, with the fresh warmth of a full-summer day...
This sentence gives us the date, the weather, and sets the tone. Efficient. Once this is done, she uses a good amount of dialogue to give color and personality to the people. In fact, as the story progresses most of the text is dialogue. The pace of the story also quickens and they begin the ritualistic stoning. Here is a sample:
The crowd was quiet. A girl whispered, "I hope it's not Nancy," and the sound of the whisper reached the edges of the crowd.
"It's not the way it used to be." Old Man Warner said clearly. "People ain't the way they used to be."
"All right," Mr. Summers said. "Open the papers. Harry, you open little Dave's."
As you can see, the dialogue moves the plot and give a sense of the personality of the characters.