What are three reasons why the townspeople of "The Lottery" continue to practice their tradition even though the original purpose has been lost?

When confronted with the information that other towns have suspended their tradition of holding the lottery,  Old Man Warner is outraged and gives a very important reason why the lottery is important. He makes a connection between the lottery and the success of the crops. 

Warner's comments suggest that the lottery is absolutely necessary to the survival of the town. He has such a firm belief that the lottery is so important a tradition that he equates it with reverting back to primitive times, it is ironic, because the lottery is a savage, primitive form of behavior.

 "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." (Jackson) 

There have been civilizations in history that believed in human sacrifice as a necessary part of their tradition.  Human sacrifice was performed to appease the gods, to honor the gods, to ask the gods, through the sacrifice, to please allow the crops to be full and heavy.  This insures the survival of the many while sacrificing the one.