Part of the eeriness of the story is that people are following blind tradition. They have no idea why they do what they do. They are powerless to change it. They just accept it. Moreover, their children follow the tradition, which means that the tradition will continue. So, in essence this town accepts ritual murder every year.
The only slight clue as to the origins of the lottery is Old Man Warner's words that if they stop it, life in the town will turn out badly. In particular, corn will not come up. So, our best guess is that the lottery is rooted in the agricultural rhythms of society. Here is what Old Man Warner says:
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. "Bad enough to see young Joe Summers up there joking with everybody."
In conclusion, the blind follow the blind and there is nothing in the story to suggest that this will stop.