When people are happy they celebrate different occasions. Some occasions are functions and some occasions are religious and some traditional. People celebrate these occasions according to their customs and traditions and according to the environments and conditions of that country. So far your question that why do people celebrate wedding anniversary can be explained in the following way. We all know that fashion of celebrating wedding anniversary first stared in Europe and U.S.A and then spread in the Eastern countries as well as the whole world. Infact when couples are married and they experience a happy life after marriage, this event of wedding anniversary reminds them of their sweet memories of the last one-year of their marriage. In the memories of those sweet moments this event becomes more or less essential to be celebrated. Friends and relatives are gathered and happy couples invite them to share their happiness and joys of married life. So simply we can say wedding anniversary is celebrated just to renew one's happy married life and share the joys with others.