While Tessie Hutcherson, the eventual victim, is late to the lottery, the only character not in attendance is Clyde Dunbar, who broke his leg.
Shirley Jackson seems to include this detail to explain about the "traditional" values held in this village. There is an interesting exchange that explains much about these values. Mr. Summers, the man who conducts the lottery, seems a bit bothered by the fact that Janey Dunbar was going to draw for her husband. He asks, "Don't you have a grown boy to do it for you, Janey?"
The narrator excuses this as a formality ("Although Mr. Summers and everyone else in the village knew the answer perfectly well, it was the business of the official of the lottery to ask such questions formally."), but the patriarchy in this village is evident as the next person to draw is the eldest son of Ms. Watson. Mr. Summers responds to the tall boy by saying, "Glad to see your mother's got a man to do it."
It's important to remember that in a story as spare as "The Lottery" each detail is important. This seemingly throwaway detail allows the reader to understand much more about the village where this story is set. Perhaps, like the lottery itself, Jackson includes this seemingly unimportant detail to comment on traditional values, like patriarchy.