The answer to this question lies in the way that tradition is presented in this short story and how it is shown to be a force that people unthiningly cling on to no matter what evidence is presented to suggest that it is something that can be harmful. This is most strongly seen in the character of Old Man Warner, who seems to have the function of being the representative of tradition in this story, as he is both the oldest inhabitant of the village and a staunch defendant of the lottery. Note how he defends the practice of the lottery as he scornfully derides other villages that now no longer practice the lottery:
Listening to the young folks, nothing's good enough for them. Next htink 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...
Note the way that he defends the lottery. He equates anybody that argues with it as wanting to go back in time to primitive living and then justifies his argument on the saying that he quotes. Finally he turns to peevishness to express his argument. For him, and so often for us, Jackson seems to be saying, our social behaviour is dictated far more by what we have always done than what is actually best for us. Tradition rules.