There are several hints given in the story about why the village still participates in the lottery, but the main reason seems to be that it's always been done that way, and no one questions or analyzes it.
"The original paraphernalia for the lottery had been lost long ago, and the black box now resting on the stool had been put into use even before Old Man Warner, the oldest man in town, was born. Mr. Summers spoke frequently to the villagers about making a new box, but no one liked to upset even as much tradition as was represented by the black box."
In this quote from Shirley Jackson's short story, "The Lottery," readers understand that the villagers have been participating in the lottery as long as anyone can remember. The town's civic leader, Mr. Summers, encourages the villagers to adopt a new box for conducting the lottery, but no one wants to change even this small detail. This shows how resistant they are to change. They have a this-is-the-way-we've-always-done-it mentality. They did let go of some of the minor aspects of the tradition of the lottery, such as the official chanting before the lottery, but they wouldn't let go of something as significant as the box.
"The people had done it so many times that they only half listened to the directions: most of them were quiet. wetting their lips. not looking around."
This quote also shows that the villagers participate in the lottery as a blind routine. It's something they have always done. A few mention that other villages have talked about stopping lotteries, but their commitment to this idea is slim. They lack the verve, courage, perhaps even the interest, to pursue ending the lottery. Consider the following quote:
" 'They do say,' Mr. Adams said to Old Man Warner, who stood next to him, 'that over in the north village they're talking of giving up the lottery.' Old Man Warner snorted. 'pack of crazy fools,' he said. 'Listening to the young folks, nothing's good enough for them. Next thing you know, they'll be wanting to go back to living in caves, nobody work any more, live that way for a while. Used to be a saying about Lottery in June, corn be heavy soon. First thing you know, we'd all be eating stewed chickweed and acorns. There's always been a lottery,' he added petulantly"
Old man Warner adds that it is his seventy-seventh time to be in a lottery. This is said as a source of pride for him, possibly because he's survived that many lotteries. He says there is "nothing but trouble" in ending lotteries. He doesn't elaborate on that idea, but one could infer because of retort "Pack of crazy fools. Listening to the young folks," that it is an idea that is a folly of youth. He insinuates that the outcome of ending lotteries would be unsavory.
"Although the villagers had forgotten the ritual and lost the original black box, they still remembered to use stones."
This quote suggests that it is not the tradition itself that is important to the villagers. It is as if the brutality of it, the selective destruction, is what matters to them. The only one who cries out against it is Tessie, whose name is drawn and is the one who will be stoned. No one comes to her defense, and no one agrees with her claims that it isn't fair.