The most interesting thing about the story is that the villagers keep up the tradition of stoning someone once a year, but they do not actually know why they should continue this savage and cruel act.  In fact, some villages stop this practice.  When people in this village hear of it, they generally resist for two reasons. 

First, tradition is an important part of this culture.  In other words, because they have done it in the past is a strong argument for why they should continue it in the present and future. We get this sense, because they do not even want to replace the black box, even though it is in bad condition. They should continue the lottery, because they have been doing it. 

Second, there is some indication that some might believe that conducting the lottery is necessary for a good harvest.  Old Man Warner, the oldest man in the village says these words:

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 hat way for a while. Used to be a saying about 'Lottery in June, corn be heavy soon.'